Spiro[2.4]heptanes for Treatment of Flaviviridae Infections

ABSTRACT

Compounds, methods, and compositions for the treatment of infections in or exposure to humans and other host animals of Flaviviridae viruses, including HCV, that includes the administration of an effective amount of a spiro[2.4]heptane as described herein or a pharmaceutically acceptable salt or prodrug thereof, optionally in a pharmaceutically acceptable carrier, are provided. The spiro[2.4]heptane compounds either possess antiviral activity, or are metabolized to a compound that exhibits such activity.

RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.14/162,618 file Jan. 23, 2013, which is a division of U.S. patentapplication Ser. No. 13/767,042 filed Feb. 14, 2013 that granted as U.S.Pat. No. 8,673,926 on Mar. 18, 2014, which claims the benefit ofpriority of U.S. Provisional Application No. 61/615,989 filed Mar. 27,2012, U.S. Provisional Application No. 61/615,975 filed Mar. 27, 2012,and U.S. Provisional Application No. 61/598,524 filed Feb. 14, 2012. Theentirety of each of these applications is incorporated herein byreference.

GOVERNMENT INTEREST

This invention was made with government support under grant AI25899awarded by the U.S. Public Health Service, National Institute of Allergyand Infectious Diseases, NIH. The government has certain rights in theinvention.

FIELD OF THE INVENTION

The present invention is in the field of compounds and their uses andcompositions to treat viral infections, especially Flaviviridae viruses,including Hepatitis C Virus (HCV), as well as other related conditions.

BACKGROUND OF THE INVENTION

Flaviviridae are a family of RNA viruses with a single stranded positivesense RNA genome. The RNA viral genome plays important roles duringviral replication, including as mRNA for viral protein synthesis, atemplate for RNA replication, and a nascent RNA genome for a newlyformed virus. The family includes the genera Flavivirus, Hepacivirus,Hepatitis G Virus, and Pestivirus.

Major diseases caused by Flaviviridae include hepatitis C, Dengue fever,West Nile encephalitis, Tick-borne encephalitis, and Yellow fever.

Hepatitis C (HCV) is a Hepacivirus. It is estimated that 75% of allcases of liver disease is caused by HCV. HCV infection can lead tocirrhosis and liver cancer and can become so serious that a livertransplant is required. Approximately 170-200 million people worldwideare infected, with 3-5 million in the United States.

The HCV non-structural protein NS5B RNA-dependent RNA polymerase is akey component of the replicative complex and is responsible forinitiating and catalyzing viral RNA synthesis. As a result, the HCV NS5Bis an attractive target for the current drug discovery and developmentof anti-HCV agents. There are two major subclasses of NS5B inhibitors:nucleoside analogs, which are anabolized to their active triphosphates,and which act as alternative substrates for the polymerase, andnon-nucleoside inhibitors (NNIs), which bind to allosteric regions onthe protein. Nucleoside or nucleotide inhibitors mimic naturalpolymerase substrate and act as chain terminators. They inhibit theinitiation of RNA transcription and elongation of a nacent RNA chain.

Other HCV proteins that are targets for therapeutic approaches areNS3/4A (a serine protease) and NS5A (a non-structural protein that is anessential component of HCV replicase and exerts range of effects oncellular pathways).

Current approved therapies for HCV include interferon alpha-2b orpegylated interferon alpha-2b (Pegintron), which is administered withribavirin (Rebetol), and NS3/4A protease inhibitors telaprevir (Incivek,Vertex and Johnson & Johnson) and boceprevir (Victrelis, Merck).

Several NS5B nucleoside/nucleotide polymerase inhibitors have been inclinical trials (shown in FIG. 1). 2′-C-methylcytidine (NM107), thevaline ester of 2′-C-methylcytidine (valocitabine, NM283), was the firstpolymerase inhibitors in clinical trials and was discontinued due to theGI toxicity. The second nucleoside inhibitor, 4′-C-azido-nucleoside(R1479) as its tri-isobutyl ester prodrug (R1626), has been developed byRoche, however, it was discontinued due to the haematopoetic toxicity.Currently, Roche and Pharmasset are developing R7128 (mericitabine), aprodrug of β-D-2′-deoxy-2′-α-fluoro-2′-C-methylcytidine (PSI6130).Idenix has been developing a purine analogue, 2′-C-methylguanosinemonophosphate prodrug (IDX184), however, it is currently under clinicalhold due to the potential cardiac toxicity concern by the FDA because ofthe discontinuation of Inhibitex INX-189 due to cardio-toxicity. Auridine analogue in a prodrug (PSI-7977) form can potently inhibit HCVreplication. Recently, a 3′,5′-cyclic phosphate analogue, PSI-938, hasalso been reported as a potent anti-HCV agent but has been discontinueddue to liver toxicity.

Oh et al. published an article on “Design and Synthesis of NovelCarbocyclic Versions of 2′-Spirocyclopropyl ribonucleosides as potentanti-HCV agents.” Oh et al. reported that the synthesized cytosinenucleoside had moderate anti-HCV activity (IC₅₀ of 14.4 in Hu7 cellline).

Gadthula et al. published an article on “Synthesis and antiviralactivity of cyclopropy-spirocarbocyclic adenosine(4R,5S,6R,7R)-4-(6-amino-9H-pur-9-yl)-7-(hydroxymethyl)spiro[2.4]heptane-5,6diol against hepatitis C virus” (Bioorganic & Medicinal ChemistryLetters 21 (2011) 3982-3985). The titled compound exhibited an EC₅₀ of0.273 and 0.368 μM in genotypes 1A and 1B, respectively in the Hu7 RNAreplicon assay.

United States patents which describe nucleoside polymerase inhibitorsfor the treatment of Flaviviridae, including HCV, include those filed byIdenix Pharmaceuticals (U.S. Pat. Nos. 8,343,937; 8,299,038; 6,914,054;6,812,219; 7,608,597; 7,902,202; 7,951,789; 7,547,704; 7,456,155;7,365,057; 7,608,600; 7,635,689; 7,625,875; 7,148,206; 7,163,929;7,169,766; 7,105,493; and 7,157,441), Merck (U.S. Pat. Nos. 7,125,855;6,777,395; 7,105,499; and 7,202,224), Gilead Sciences (U.S. Pat. Nos.7,973,013; 8,324,179; and 8,334,270), Emory University (U.S. Pat. Nos.6,911,424; 8,168,583; 6,348,587; 7,662,938; and 7,307,065), andPharmasset Inc. (U.S. Pat. Nos. 7,429,572; 8,093,380; 7,964,580; and6,949,522).

There remains a strong medical need to develop anti-Flaviviridae,including anti-HCV, therapies that are effective, well-tolerated, andreasonably safe. Given the number of people infected with hepatitis Cand the potential severity of the infection, the need is particularlystrong. The need is accentuated by the expectation that combination drugtherapies may be most efficacious to treat HCV and other Flaviviridae.

It is therefore an object of the present invention to provide compounds,pharmaceutical compositions, and methods and uses to treat and/orprevent infections from Flaviviridae viruses, including Hepatitis Cvirus, and related conditions and/or disease states as otherwisedescribed herein.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a number of nucleoside/nucleotide polymerase inhibitorswhich are or have been in clinical trials.

FIGS. 2-11 provide various processes for the preparation of thespiro[2.4] compounds of the invention.

FIG. 2 Reagents and Conditions: (a) (Boc)₂O, DMAP, THF; 80% yield; (b)Savinase, THF, Buffer solution; 84% yield; (c) OsO₄, NMO, Acetone; 72%yield; (d) i) BzCl, Pyridine; 86% yield, ii) NaBH₄, Methanol; 83% yield;(e) HCl/Ether, Methanol; 90% yield; (f) NaNO₂, CH₃COOH, Water,Acetonitrile; 54% yield; (g) NaOMe, Methanol; 78% yield; (h) (i)2,2-dimethoxy propane, PTSA, Acetone, (ii) TBDMSCl₂, Imidazole, DCM,(iii) mCPBA, DCM; 86% yield; (i) n-BuLi, trimethylsulfonium iodide, THF;(j) (i) Desmortine, DCM; (ii) NaBH₄, CeCl₃.7H₂O, MeOH; (k) Diethyl ZincMeI₂, Ether; (l) Base, DIAD, TPP, THF; 70% yield; (m) TFA, TBAF/THF 90%yield; (n) Phosphoramidate chloride, NMI, THF; (o) DPPA, DIAD, TPP, THF;(p) methoxyacrylol isocyanate, THF; (q) NH₄OH, 1,4-dioxane/EtOH, steelbomb, 90-100° C.; (r) THF/H₂O; (s) Phosphoramidate chloride, NMI, THF.

FIG. 3 Reagents and Conditions: (a) BnCl, NaH, DMF; (b) TFA, TBAF/THF;(c) TBDMSCl₂, Imidazole, DCM; (d) DAST, DCM; (e) BCl₃, DCM; (f) Base,DIAD, TPP, THF; (g) TFA, TBAF/THF; (h) Base, DIAD, TPP, THF; (i) (i)NH₃/Methanol; (ii) TFA, TBAF/THF.

FIG. 4 Reagents and Conditions: (a) PCC, DCM; (b) BCl₃, DCM; (c) Base,DIAD, TPP, THF; (d) CH₃Li, THF; (e) DAST, DCM; (f) TFA, TBAF/THF.

FIG. 5 Reagents and Conditions: (a) BnCl, NaH, DMF; (b) TFA, TBAF/THF;(c) TBDMSCl₂, Imidazole, DCM (d) DAST, DCM; (e) BCl₃, DCM; (f) Base,DIAD, TPP, THF; (g) TFA, TBAF/THF.

FIG. 6 Reagents and Conditions: (a) i) NaNO₂, CH₃COOH, waterAcetonitrile; ii) NaOMe, Methanol; (b) TIDPSCl₂, Imidazole, DCM; (c)mCPBA, DCM; (d) BzCl, Pyridine; (e) Trimethyl sulfonium Iodide, nBuLi,THF; (f) Diethyl Zinc, MeI₂ ether; (g) Base (Purine or pyrimidine),DIAD, TPP, THF; (h) NaOMe, Methanol; (i) TBAF, Acetic acid, THF; (j)PDC, DCM; (k) CH₃MgBr, ether; (l) TBAF, Acetic acid, THF; (m) DAST, DCM;(n) TBAF, Acetic acid, THF; (o) i) Tf₂O, Py; ii) CeOAc, benzene; (p)NaOMe, Methanol; (q) DAST, DCM; (r) TBAF, Acetic acid, THF.

FIG. 7 Reagents and Conditions: (a) Trimethyl sulfonium Iodide, nBuLi,THF; (b) Base (Purine or pyrimidine), DIAD, TPP, THF; (c) NaOMe,Methanol; (d) PDC, DCM; (e) CH₃MgBr, ether; (f) TBAF, Acetic acid, THF;(g) DAST, DCM; (h) TBAF, Acetic acid, THF.

FIG. 8 Reagents and Conditions: (a) i) NaNO₂, CH₃COOH, waterAcetonitrile; ii) NaOMe, Methanol; (b) TIDPSCl₂, Imidazole, DCM; (c)mCPBA, DCM; (d) BzCl, Pyridine; (e) Trimethyl sulfonium Iodide, nBuLi,THF; (f) Base (Purine or pyrimidine), DIAD, TPP, THF; (g) NaOMe,Methanol; (h) TBAF, Acetic acid, THF; (i) PDC, DCM; (j) CH₃MgBr, ether;(k) TBAF, Acetic acid, THF; (l) DAST, DCM; (m) TBAF, Acetic acid, THF;(n) i) Tf₂O, Py; ii) CeOAc, benzene; (o) NaOMe, Methanol; (p) DAST, DCM;(q) TBAF, Acetic acid, THF.

FIG. 9 shows how to prepare β-L spiro[2.4]heptanes of the presentinvention.

FIG. 10 Reagents and Conditions: (a) Diethyl Zinc MeI₂, Ether; (b) BnCl,NaH, DMF; (c) (i) TFA, TBAF/THF; (ii) TBDMSCl₂, Imidazole, DCM; (d) PCC,DCM; (e) CH₃Li, THF; (f) DAST, DCM; (g) BCl₃, DCM; (h) Benzoic acid,DIAD, TPP, THF; (i) Base, DIAD, TPP, THF; (j) TFA, TBAF/THF.

FIG. 11 Reagents and Conditions: (a) CH₃Li, THF or CH₃MgCl, THF; (b)Actyl chloride, DIMAP, DCM; (c) BCl₃, DCM; (d) Base, DIAD, TPP, THF; (e)NaOMe, MeOH; (f) TFA, TBAF/THF.

SUMMARY OF THE INVENTION

Compounds, methods, and compositions are provided for the treatment of ahost infected with a Flaviviridae virus (for example, a Flavivirus,Hepacivirus, Hepatitis G Virus, or Pestivirus), and more particularly,Hepatitis C, Dengue fever, West Nile encephalitis, Tick-borneencephalitis, or Yellow fever. The compounds and compositions can alsobe used to treat related conditions such as anti-Flaviviridae (forexample, anti-HCV) antibody positive and antigen positive conditions,viral-based chronic liver inflammation, liver cancer resulting fromadvanced hepatitis C, cirrhosis, chronic or acute hepatitis C, fulminanthepatitis C, chronic persistent hepatitis C and anti-Flaviviridae-basedfatigue. The compound or formulations that include the compounds canalso be used prophylactically to prevent or retard the progression ofclinical illness in individuals who are anti-Flaviviridae (for example,anti-HCV) antibody or antigen positive or who have been exposed to aFlaviviridae, such as hepatitis C.

The invention includes using an effective amount for a host in needthereof of the spiro[2.4]heptane of Formula I or II (which have a β-Dtype configuration with reference to a corresponding nucleoside) or apharmaceutically acceptable composition, salt, or prodrug thereof:

wherein:

-   R¹ is a natural or non-natural heteroaryl or heterocyclic moiety,    which can be a pyrimidine or purine, for example cytosine,    5-halocytosine (for example, 5-fluorocytosine or 5-iodocytosine),    uracil, 5-halouracil (for example, 5-fluorouracil or 5-iodouracil),    5-methylcytosine, thymine, adenine, thymine, guanine, xanthine, or    hypoxanthine;-   R² is C₁-C₄ alkyl or substituted alkyl (for example methyl), F, Cl,    N₃, or OR⁷;-   R³ is C₁-C₄ alkyl or substituted alkyl, (for example methyl), F, Cl,    N₃, or OR⁷;-   R⁴ is OR⁷, H, C₁-C₄ alkyl (for example methyl), F, Cl, or N₃;-   R⁵ is H; phosphate (including mono-, di- or triphosphate or a    stabilized phosphate prodrug); phosphoramidate; acyl (including    lower acyl); alkyl (including lower alkyl); sulfonate ester    including alkyl or arylalkyl sulfonyl including methanesulfonyl and    benzyl, wherein the phenyl group is optionally substituted with one    or more substituents as described in the definition of aryl given    herein; a lipid, including a phospholipid; an amino acid; a    carbohydrate; a peptide; a cholesterol; or other pharmaceutically    acceptable leaving group which when administered in vivo is capable    of providing a compound wherein R⁵ is H or (mono, di or tri)    phosphate;-   B is cytosine, 5-halocytosine (for example, 5-fluorocytosine or    5-iodocytosine), uracil, 5-halouracil (for example, 5-fluorouracil    or 5-iodouracil), 5-methylcytosine, thymine, adenine, guanine,    xanthine or hypoxanthine, or a non-natural heteroaryl or    heterocyclic moiety′-   R⁶ is H; and,-   R⁷ is H, acyl, phosphate, sulfate, amino acid, peptide, or an    oxygen-protecting group.

In one embodiment, in Formula I, R² is H and R³ is F.

In another embodiment, in Formula I either R³ and R⁴ or R⁴ and R⁵, or inFormula II R⁴ and R⁵ together form a bridge that may, for example, be aphosphoester, carbodiester or phosphoroamidate.

In an alternative embodiment, compounds, methods, and compositions areprovided for the treatment of a host infected with or exposed to aFlaviviridae virus (Hepatitis C, Dengue fever, West Nile encephalitis,Tick-borne encephalitis, or Yellow fever) described herein. Theinvention includes using an effective treatment amount for a host of thespiro[2.4]heptane of Formula III or IV (with β-L type configuration withreference to a corresponding nucleoside) or a pharmaceuticallyacceptable composition, salt or prodrug thereof:

wherein R¹, R², R³, R⁴, R⁵, R⁶, R⁷, and B are as defined above.

The compounds of the invention can be administered alone or incombination with another anti-Flaviviridae, for example an anti-HCV,drug to treat the infected host. In certain embodiments, it is useful toadminister a combination of drugs that modulates a different pathway orinhibits a different target in the virus. Since the disclosedspiro[2.4]heptanes are NS5B polymerase inhibitors, it may be useful toadminister the compound to a host in combination with a proteaseinhibitor, such as an NS3/4A protease inhibitor (for example, telaprevir(Incivek) or biceprevir (Victrelis) or an NS5A inhibitor. The compoundof the invention can also be administered in combination with astructurally different NS5B polymerase inhibitor such as anothercompound described herein or below, including Gilead's PSI-7977 orRoche's PSI-7128. The compounds of the invention can also beadministered in combination with interferon alfa-2a, which may bepegylated or otherwise modified, and/or ribavirin.

The spiro[2.4]heptanes of the invention are typically administeredorally, for example in pill or tablet form, but may be administered viaother routes which the attending physician considers appropriate,including via intravenous, transdermal, subcutaneous, topical,parenteral, or other suitable route.

DETAILED DESCRIPTION OF THE INVENTION

The invention disclosed herein is a compound, method, and compositionfor the treatment of infections in or exposure to humans and other hostanimals of the Flaviviridae viruses described herein or otherwise known,including HCV, that includes the administration of an effective amountof a spiro[2.4]heptane as described herein or a pharmaceuticallyacceptable salt or prodrug thereof, optionally in a pharmaceuticallyacceptable carrier. The compounds of this invention either possessantiviral activity, or are metabolized to a compound that exhibits suchactivity.

The compounds and compositions can also be used to treat relatedconditions such as anti-Flaviviridae antibody positive andFlaviviridae-antigen positive conditions, viral-based chronic liverinflammation, liver cancer resulting from advanced hepatitis C,cirrhosis, acute hepatitis C, fulminant hepatitis C, chronic persistenthepatitis C, and anti-Flaviviridae-based fatigue. The compounds orformulations that include the compounds can also be usedprophylactically to prevent or retard the progression of clinicalillness in individuals who are anti-Flaviviridae antibody orFlaviviridae-antigen positive or who have been exposed to aFlaviviridae, such as hepatitis C.

The present invention includes the following features:

(a) spiro[2.4]heptanes as described herein, and pharmaceuticallyacceptable salts and prodrugs thereof (in either the β-D- or β-L formwhen considered with respect to corresponding nucleoside structure);

(b) spiro[2.4]heptanes (with relative β-D- or β-L-configuration) asdescribed herein, and pharmaceutically acceptable salts and prodrugsthereof for use in the treatment or prophylaxis of a Flaviviridaeinfection, for example a hepatitis C infection;

(c) use of spiro[2.4]heptanes (with relative β-D- or β-L-configuration),and pharmaceutically acceptable salts and prodrugs thereof in themanufacture of a medicament for treatment of a Flaviviridae, forexample, a hepatitis C infection;

(d) a method for manufacturing a medicament intended for the therapeuticuse for treating a Flaviviridae infection, for example, a hepatitis Cinfection, characterized in that a spiro[2.4]heptane (with relative β-D-or β-L-configuration) as described herein is used in the manufacture;

(e) a pharmaceutical formulation comprising an effective host-treatingamount of the spiro[2.4]heptane (with relative β-D- orβ-L-configuration) or a pharmaceutically acceptable salt or prodrugthereof together with a pharmaceutically acceptable carrier or diluent;

(f) spiro[2.4]heptane (with relative β-D- or β-L-configuration) asdescribed herein substantially in the absence of the opposite enantiomerof the described compound, or substantially isolated from other chemicalentities; and,

(g) processes for the preparation of therapeutic products that containan effective amount of a spiro[2.4]heptane (with relative β-D- orβ-L-configuration), as described herein.

I. SPIRO[2.4]HEPTANES OF THE INVENTION

The spiro[2.4]heptanes of the invention are those depicted in Formula Ior II or a pharmaceutically acceptable composition, salt or prodrugthereof:

In an alternative embodiment, compounds, methods, and compositions areprovided for the treatment of a host infected with or exposed tohepatitis C or another Flaviviridae virus (for example, Dengue fever,West Nile encephalitis, Tick-borne encephalitis, or Yellow fever). Theinvention includes using an effective treatment amount for a host of thespiro[2.4]heptane of Formula III or IV (with β-L type configuration withreference to a corresponding nucleoside) or a pharmaceuticallyacceptable composition, salt, or prodrug thereof:

wherein:

-   R¹ is a natural or non-natural heteroaryl or heterocyclic moiety,    which can be a pyrimidine or purine, for example cytosine,    5-halocytosine (for example, 5-fluorocytosine or 5-iodocytosine),    uracil, 5-halouracil (for example, 5-fluorouracil or 5-iodouracil),    5-methylcytosine, thymine, adenine, thymine, guanine, xanthine or    hypoxanthine;-   R² is C₁-C₄ alkyl (for example methyl), F, Cl, N₃, or OR⁷;-   R³ is C₁-C₄ alkyl (for example methyl), F, Cl, N₃, or OR⁷;-   R⁴ is OR⁷, H, C₁-C₄ alkyl (for example methyl), F, Cl, or N₃;-   R⁵ is H; phosphate (including mono-, di- or triphosphate or a    stabilized phosphate prodrug); phosphoramidate; phosphonate; amino    acid; acyl (including lower acyl); alkyl (including lower alkyl);    sulfonate ester including alkyl or arylalkyl sulfonyl including    methanesulfonyl and benzyl, wherein the phenyl group is optionally    substituted with one or more substituents as described in the    definition of aryl given herein; a lipid, including a phospholipid;    a carbohydrate; a peptide; a cholesterol; or other pharmaceutically    acceptable leaving group which when administered in vivo is capable    of providing a compound wherein R⁵ is H or phosphate;-   B is cytosine, 5-halocytosine (for example, 5-fluorocytosine or    5-iodocytosine), uracil, 5-halouracil (for example, 5-fluorouracil    or 5-iodouracil), 5-methylcytosine, thymine, or a natural or    non-natural heteroaryl or heterocyclic moiety;-   R⁶ is H; and,-   R⁷ is H; phosphate (including mono-, di- or triphosphate or a    stabilized phosphate prodrug); phosphoramidate; phosphonate; amino    acid; acyl (including lower acyl); alkyl (including lower alkyl);    sulfonate ester including alkyl or arylalkyl sulfonyl including    methanesulfonyl and benzyl, wherein the phenyl group is optionally    substituted with one or more substituents as described in the    definition of aryl given herein; a lipid, including a phospholipid;    a carbohydrate; a peptide; a cholesterol; or other pharmaceutically    acceptable leaving group which when administered in vivo is capable    of providing a compound wherein R⁵ is H or phosphate.

In a typical embodiment, the compound is a β-D isomer with reference tothe corresponding nucleoside (i.e., in the naturally occurringconfiguration). In an alternative configuration, the compound isprovided as a β-L isomer. The compound is typically at least 95% free ofthe opposite enantiomer, and can be at least 98% or even 100% free ofthe opposite enantiomer.

In an embodiment, in Formula I, R² is H and R³ is F.

In another embodiment, either R³ and R⁴ or R⁴ and R⁵ together form abridge that may be, for example, a phosphoester, carbodiester, orphosphoramidate.

In another embodiment, either of the two —CH₂— groups in the cyclopropylring can have a substituent, for example, methyl, halogen (F, Cl, Br orI), —OH, or N₃. In general, if a substituent is placed on thecyclopropyl ring, it should be small due to potential steric hindrancein the position. Typically, the cyclopropyl group is unsubstituted.

In an embodiment, R¹ is a group according to the chemical formula R₁a orR₁b:

wherein:

-   X is H, —NR^(A)R^(B), halogen (F, Cl, Br or I), O, OR^(X), S or    SR^(X);-   T is N—R^(W) or C—R^(WA)R^(WB);-   V is H, O, OR^(X), S or SR^(X), a C₁-C₃ alkyl, a NR^(A)R^(B) group,    a halogen (F, Cl, Br, I), nitro, cyano, a

-    group;-   Y is C—R^(Y), N, O or S;-   Ya is H, F, Cl, Br, I, or —C₁-C₄ alkyl;-   R^(H) is absent, H, or a C₁-C₃ alkyl;-   R¹⁵ is H, F, Cl, Br, I, C₁-C₄ alkyl (often CH₃), —C≡N,    —(CH₂)_(n)—C≡C—R_(a),

-   X⁶ is H, C₁-C₄ alkyl (often, CH₃), F, Cl, Br, or I;-   R_(a) is H, F, Cl, Br, I, or —C₁-C₄ alkyl, often H or CH₃;-   n is 0, 1, 2, 3, 4, 5 (often 0 or 1);-   R^(W) is absent, H, or a C₁-C₃ alkyl group;-   R^(WA) is H or a C₁-C₃ alkyl group;-   R^(WB) is absent, H, or a C₁-C₃ alkyl group;-   R^(Y) is H, a C₁-C₃ alkyl group, a halo group (F, Cl, Br or I),    nitro, cyano, or a

-    group;-   R^(A), R^(B), and R^(X) are each independently H, an acyl group, a    C₁-C₂₀ alkyl or ether group, or an amino acid residue (D or L); and-   R^(ac) is H or a C₁-C₃ alkyl group which is optionally substituted    with 1 or 2 hydroxyl groups or from 1 to 3 halogens (when    substituted, R^(ac) is often substituted with 3 fluoro groups).

In certain aspects of the invention of any of the spiro[2.4]heptanesdescribed herein, R¹ is according to the formula:

wherein R¹⁵ and R^(A) are the same as described above. R¹⁵ is often H,CH₃, or F, more often H, and R^(A) is an acyl group as otherwisedescribed herein or a C₁-C₆ alkyl group, in certain instances, acyclopropyl group.

In still other embodiments, R₁ is uracil, thymine, cytosine,5-methylcytosine, 7-deazaadenine, guanine, xanthine, or hypoxanthine. Insome embodiments, B is uracil, cytosine, or guanine. Alternatively, incertain embodiments, B is cytosine, uracil, thymine, or guanine, whereR^(A) is H, an acyl group, a C₁-C₂₀ alkyl or ether group, or an aminoacid residue (D or L) as described above.

In another embodiment, the compound is according to the chemicalformula:

wherein:

-   R¹ is as described above, and typically cytosine, 5-methylcytosine,    5-fluorocytosine, 5-iodocytosine, uracil, thymine, 5-fluorouracil,    or 5-iodouracil;-   R″ is H or N₃ (often H);-   X and X′ are each independently H, C₁-C₄ alkyl (often CH₃), OR^(MA),    or a halogen (often F or Cl, more often F);-   R¹¹ is H, an acyl group, a C₁-C₂₀ alkyl or ether group or an amino    acid residue (D or L), a peptide residue, a lipid (including    phospholipid), cholesterol or cholesterol derivative, a    carbohydrate, phosphate, diphosphate, triphosphate, phosphodiester,    or phosphoramidate group, or together, R¹ and the hydroxyl group at    the 3′ position of the sugar moiety form a carbodiester,    phosphodiester, or phosphoramidate group with the oxygen atoms to    which they are bonded;-   R^(MA) is H, a C₁-C₄ alkyl group (if alkyl, often CH₃), an acyl    group (often, a C₂-C₂₁ optionally substituted acyl group), an amino    acid residue (D or L), or together with the oxygen atom to which    R^(M) is attached forms a carbodiester, phosphodiester, or    phosphoramidate group with the oxygen atom to which R^(MA) is    attached; and,-   R^(M) is H, a C₁-C₄ alkyl group (if alkyl, often CH₃), an acyl group    (often, a C₂-C₂₁ optionally substituted acyl group), an amino acid    residue (D or L), or together with the oxygen atom to which R^(MA)    or R¹¹ is attached forms a carbodiester, phosphodiester, or    phosphoramidate group with the oxygen atom to which R^(M) is    attached, or its pharmaceutically acceptable salt.

In another embodiment, the compound is according to the chemicalformula:

wherein:

-   R″ is H or N₃ (often H);-   X is H, OR^(MA), or a halogen (often F);-   R^(A) is H, an acyl group, an alkyl or ether group, or an amino acid    residue (D or L);-   R¹¹ is H, an acyl group, an alkyl or ether group, or an amino acid    residue (D or L), a peptide residue, a lipid (including    phospholipid), cholesterol or cholesterol derivative, a    carbohydrate, phosphate, diphosphate, triphosphate, phosphodiester    or phosphoramidate group, or together with the oxygen to which R^(M)    is attached form a carbodiester, phosphodiester, or phosphoramidate    group with the oxygen to which R¹¹ is attached;-   R^(MA) is H, a C₁-C₄ alkyl group (if alkyl, often CH₃), an acyl    group (often, a C₂-C₂₁ optionally substituted acyl group), an amino    acid residue (D or L), or together with the oxygen atom to which    R^(M) is attached forms a carbodiester, phosphodiester, or    phosphoramidate group with the oxygen atom to which R^(MA) is    attached; and    R^(M) is H, a C₁-C₄ alkyl group (if alkyl, often CH₃), an acyl group    (often, a C₂-C₂₁ optionally substituted acyl group), an amino acid    residue (D or L), or together with the oxygen atom to which R^(MA)    or R¹¹ is attached forms a carbodiester, phosphodiester, or    phosphoramidate group with the oxygen atom to which R^(M) is    attached, or a pharmaceutically acceptable salt thereof. Often    R^(MA) and R^(M) are both H.

In another embodiment, the compound is according to the formula:

wherein

-   X is OH or F;-   R^(A) is H, an acyl group, a C₁-C₂₀ alkyl or ether group or an amino    acid residue (D or L) (R^(A) is often H); and-   R¹¹ is H, an acyl group, a C₁-C₂₀ alkyl or ether group, or an amino    acid residue (D or L), a peptide residue, a lipid (including    phospholipid), cholesterol or cholesterol derivative, a    carbohydrate, phosphate, diphosphate, triphosphate, phosphodiester,    or phosphoramidate group, or R¹¹ and the hydroxyl group at the    3′-position of the sugar together form a carbodiester,    phosphodiester, or phosphoramidate group with the oxygen atoms to    which they are bonded, or a pharmaceutically acceptable salt    thereof.

In another embodiment, the compound is according to the formula:

wherein:

-   R^(A) is H, an acyl group, a C₁-C₂₀ alkyl or ether group, or an    amino acid residue (D or L); and-   R¹¹ is H, an acyl group, a C₁-C₂₀ alkyl or ether group, or an amino    acid residue (D or L), a peptide residue, a lipid (including    phospholipid), cholesterol or cholesterol derivative, a    carbohydrate, phosphate, diphosphate, triphosphate, phosphodiester,    or phosphoramidate group, or a pharmaceutically acceptable salt    thereof.

In still another embodiment, the compound is according to the chemicalstructure:

wherein:

-   R″ is H or N₃;-   X is OR^(MA) or a halogen (often For Cl, more often F);

X′ is H or a C₁-C₄ alkyl group (often CH₃);

-   R^(A) is H, an acyl group, a C₁-C₂₀ alkyl or ether group, or an    amino acid residue (D or L) (R^(A) is often H);-   R¹¹ is H, an acyl group, a C₁-C₂₀ alkyl or ether group, or an amino    acid residue (D or L), a peptide residue, a lipid (including    phospholipid), cholesterol or cholesterol derivative, a    carbohydrate, phosphate, diphosphate, triphosphate, phosphodiester,    or phosphoramidate group, or R¹¹ and R^(M) together form a    carbodiester, phosphodiester, or phosphoramidate group with the    oxygen atoms to which they are bonded;-   R^(MA) is H, a C₁-C₄ alkyl group (if alkyl, often CH₃), an acyl    group (often, a C₂-C₂₁ optionally substituted acyl group, more often    a C₂-C₁₀ acyl group), an amino acid residue (D or L), or together    with R^(M) forms a carbodiester, phosphodiester, or phosphoramidate    group with the oxygen atoms to which R^(M) and R^(MA) are attached;    and,-   R^(M) is H, a C₁-C₄ alkyl group (if alkyl, often CH₃), an acyl group    (often, a C₂-C₂₁ optionally substituted acyl group), an amino acid    residue (D or L), or together with R^(MA) or R¹¹ forms a    carbodiester, phosphodiester, or phosphoramidate group with the    oxygen atom to which R^(M) and R^(MA) or R¹¹ is attached, or a    pharmaceutically acceptable salt or epimer thereof. Often R^(MA) and    R^(M) are both H.

In another embodiment, the compound is according to the formula:

wherein:

-   R″ is H or N₃ (often H);-   X is OR^(MA) or a halogen (often For Cl, more often F);-   X′ is H, a C₁-C₄ alkyl group (often CH₃);-   R¹⁵ is H, F, I, or a C1-C4 alkyl group, including a CF₃ group;-   R¹¹ is H, an acyl group, a C₁-C₂₀ alkyl or ether group, or an amino    acid residue (D or L), a peptide residue, a lipid (including    phospholipid), cholesterol or cholesterol derivative, a    carbohydrate, phosphate, diphosphate, triphosphate, phosphodiester    or phosphoramidate group, or together R¹¹ and R^(M) form a    carbodiester, phosphodiester, or phosphoramidate group with the    oxygen atoms to which they are bonded;-   R^(MA) is H, a C₁-C₄ alkyl group (if alkyl, often CH₃), an acyl    group (often, a C₂-C₂₁ optionally substituted acyl group, more often    a C₂-C₁₀ acyl group), an amino acid residue (D or L), or together    with R^(M) forms a carbodiester, phosphodiester, or phosphoramidate    group, with the oxygen atoms to which R^(M) and R^(MA) are attached;    and,-   R^(M) is H, a C₁-C₄ alkyl group (if alkyl, often CH₃), an acyl group    (often, a C₂-C₂₁ optionally substituted acyl group), an amino acid    residue (D or L), or together with R^(MA) or R¹¹ forms a    carbodiester, phosphodiester, or phosphoramidate group with the    oxygen atom to which R^(M) and R^(MA) or R¹¹ is attached, or a    pharmaceutically acceptable salt thereof. Often R^(MA) and R^(M) are    both H.

In particular embodiments,

-   -   (i) in Formula I, R¹ is purine or pyrimidine; R² is CH₃ (or        wherein any of the H of CH₃ are replaced with F, including CF₃);        R³ is OH or F; R⁴ is OH; and R⁵ is H, phosphate (mono, di or        tri), or phosphoramidate;    -   (ii) in Formula I, R¹ is cytosine, 5-halocytosine (for example,        5-fluorocytosine), uracil, 5-halouracil (for example,        5-fluorouracil) or thymine; R² is CH₃ (or wherein any of the H        of CH₃ are replaced with F, including CF₃); R³ is OH or F; R⁴ is        OH; and R⁵ is H, phosphate (mono, di or tri), or        phosphoramidate;    -   (iii) in Formula I, R¹ is adenine, guanine, xanthine, or        hypoxanthine; R² is CH₃ (or wherein any of the H of CH₃ are        replaced with F, including CF₃); R³ is OH or F; R⁴ is OH; and R⁵        is H, phosphate (mono, di or tri), or phosphoramidate;    -   (iv) in Formula I, R¹ is uridine or cytosine; R² is CH₃; R³ is        OH; R⁴ is OH; and R⁵ is H, phosphate (mono, di or tri), or        phosphoramidate;    -   (v) in Formula I, R¹ is uridine or cytosine; R² is CH₃; R³ is F;        R⁴ is OH; and R⁵ is H, phosphate (mono, di or tri), or        phosphoramidate;    -   (vi) in Formula I, R¹ is uridine or cytosine; R² is H; R³ is F;        R⁴ is OH; and R⁵ is H, phosphate (mono, di or tri), or        phosphoramidate;    -   (vii) in Formula I, R¹ is 5-fluorouridine or 5-fluorocytosine;        R² is CH₃; R³ is OH; R⁴ is OH; and R⁵ is H, phosphate (mono, di        or tri), or phosphoramidate;    -   (viii) in Formula I, R¹ is 5-fluorouridine or 5-fluorocytosine;        R² is CH₃; R³ is F; R⁴ is OH; and R⁵ is H, phosphate (mono, di        or tri), or phosphoramidate;    -   (ix) in Formula I, R¹ is 5-fluorouridine or 5-fluorocytosine; R²        is H; R³ is F; R⁴ is OH; and R⁵ is H, phosphate (mono, di or        tri), or phosphoramidate;    -   (x) in Formula I, either R² is F and R³ is H or R² is H and R³        is F;    -   (xi) in Formula I, R² is CH₃ and R³ is OH or F;    -   (xii) in Formula II, B is uridine or cytosine; R⁶ is H; and R⁵        is H, phosphate (mono, di or tri), or phosphoramidate;    -   (xiii) in Formula II, B is uridine; R⁶ is H; and R⁵ is        phosphoramidate;    -   (xiv) in Formula II, B is cytosine; R⁶ is H; and R⁵ is        phosphoramidate;    -   (xv) in Formula I or II, R⁵ is phosphoramidate;    -   (xvi) in Formula I, R¹ is a non-natural heteroaryl or        heterocyclic moiety;    -   (xvii) in Formula II, B is a non-natural heteroaryl or        heterocyclic moiety;    -   (xviii) in Formula I, R² and R³ are fluoro;    -   (xix) in Formula I or II, R⁵ and R⁷ form a bridge;    -   (xx) in Formula I or II, R⁵ and R⁷ are both amino acids; and,    -   (xxi) in Formula I or II, R⁵ is a phosphoramidate and R⁷ is an        amino acid or other oxygen-protecting group.

In alternative embodiments of compounds (i) through (xxi), Formula IIIor IV is used in place of either Formula I or II.

Since Flaviviridae are positive stranded RNA viruses, in one embodiment,an R¹ or B is selected which the host would mimic or be related to anRNA base, such as uracil, cytosine, guanine, or adenosine, or a basethat is easily metabolized to an RNA base. In an alternative embodiment,the active spiro[2.4]heptane has an R¹ or B that is a derivative of anRNA base, for example, a prodrug of uracil, cytosine, guanine, oradenosine or a halogenated, alkylated, phosphorylated, or acylatedderivative.

II. DEFINITIONS

The following terms are used to describe the present invention. Ininstances where a term is not specifically defined herein, that term isgiven an art-recognized meaning by those of ordinary skill applying thatterm in context to its use in describing the present invention.

The term “pharmaceutically acceptable salt or prodrug” is usedthroughout the specification to describe any pharmaceutically acceptableform (such as an ester, phosphate ester, salt of an ester, or a relatedgroup) of a spiro[2.4]heptane which, upon administration to a patient,provides the desired active compound. Examples of pharmaceuticallyacceptable salts are organic acid addition salts formed with acids,which form a physiological acceptable anion, for example, tosylate,methanesulfonate, acetate, citrate, malonate, tartarate, succinate,benzoate, ascorbate, α-ketoglutarate, and α-glycerophosphate. Suitableinorganic salts may also be formed, including sulfate, nitrate,bicarbonate, and carbonate salts. Pharmaceutically acceptable salts maybe obtained using standard procedures well known in the art, for exampleby reacting a sufficiently basic compound such as an amine with asuitable acid affording a physiologically acceptable anion. Alkali metal(for example, sodium, potassium, or lithium) or alkaline earth metal(for example calcium) salts of carboxylic acids can also be made.

Pharmaceutically acceptable prodrug refers to a compound that ismetabolized, for example hydrolyzed or oxidized, in the host to form thecompound of the present invention. Typical examples of prodrugs includecompounds that have biologically labile protecting groups on afunctional moiety of the active compound. Prodrugs include compoundsthat can be oxidized, reduced, aminated, deaminated, hydroxylated,dehydroxylated, hydrolyzed, dehydrolyzed, alkylated, dealkylated,acylated, deacylated, phosphorylated, dephosphorylated, ordephosphoamidated to produce the active compound. The compounds of thisinvention possess antiviral activity against Flaviviridae, or aremetabolized to a compound that exhibits such activity. Thespiro[2.4]heptane can also be administered as a 5′-phosphoether lipid ora 5′-ether lipid, or a “SATE” derivative

The term “alkyl” shall mean within its context, a linear,branch-chained, or cyclic fully saturated hydrocarbon radical or alkylgroup which may be optionally substituted (for example, with halogen,including F).

The term “alkenyl” refers to a non-aromatic hydrocarbon group whichcontains at least one double bond between adjacent carbon atoms and asimilar structure to an alkyl group as otherwise described herein. Forexample, a vinyl group is an alkenyl group as otherwise describedherein.

The term “alkynyl” refers to a non-aromatic hydrocarbon group containingat least one triple bond between adjacent carbon atoms and a similarstructure to an alkyl group as otherwise described herein.

The term “substituted” indicates that the moiety may have at least oneadditional substituent, including but not limited to halogen (F, Cl, Br,I), OH, methyl, CF₃, phenyl, benzyl, N₃, alkyl, alkenyl, alkynyl, etc.

The term “aryl” or “aromatic”, in context, refers to a substituted (asotherwise described herein) or unsubstituted monovalent aromatic radicalhaving a single ring (e.g., benzene, phenyl, benzyl) or condensed rings(e.g., naphthyl, anthracenyl, phenanthrenyl, etc.) and can be bound tothe compound according to the present invention at any available stableposition on the ring(s) or as otherwise indicated in the chemicalstructure presented.

A heteroaryl ring system is a saturated or unsaturated ring with one ormore nitrogen, oxygen, or sulfur atoms in the ring (monocyclic)including but not limited to imidazole, furyl, pyrrole, furanyl, thiene,thiazole, pyridine, pyrimidine, pyrazine, triazole, oxazole, or fusedring systems such as indole, quinoline, etc., among others, which may beoptionally substituted as described above. Heteroaryl groups includenitrogen-containing heteroaryl groups such as pyrrole, pyridine,pyridone, pyridazine, pyrimidine, pyrazine, pyrazole, imidazole,triazole, triazine, tetrazole, indole, isoindole, indolizine, purine,indazole, quinoline, isoquinoline, quinolizine, phthalazine,naphthyridine, quinoxaline, quinazoline, cinnoline, pteridine,imidazopyridine, imidazotriazine, pyrazinopyridazine, acridine,phenanthridine, carbazole, carbazoline, perimidine, phenanthroline,phenacene, oxadiazole, benzimidazole, pyrrolopyridine, pyrrolopyrimidineand pyridopyrimidine; sulfur-containing aromatic heterocycles such asthiophene and benzothiophene; oxygen-containing aromatic heterocyclessuch as furan, pyran, cyclopentapyran, benzofuran and isobenzofuran; andaromatic heterocycles comprising two or more hetero atoms selected fromamong nitrogen, sulfur and oxygen, such as thiazole, thiadizole,isothiazole, benzoxazole, benzothiazole, benzothiadiazole,phenothiazine, isoxazole, furazan, phenoxazine, pyrazoloxazole,imidazothiazole, thienofuran, furopyrrole, pyridoxazine, furopyridine,furopyrimidine, thienopyrimidine and oxazole, among others, all of whichmay be optionally substituted.

The term “heterocycle” refers to a cyclic group which contains at leastone heteroatom, i.e., O, N, or S, and may be aromatic (heteroaryl) ornon-aromatic. Exemplary non-aromatic heterocyclic groups for use in thepresent invention include, for example, pyrrolidinyl, pyrrolinyl,piperidinyl, piperazinyl, N-methylpiperazinyl, imidazolinyl,pyrazolidinyl, imidazolidinyl, morpholinyl, tetrahydropyranyl,azetidinyl, oxetanyl, oxathiolanyl, pyridone, 2-pyrrolidone,ethyleneurea, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, phthalimide, andsuccinimide, among others.

In one embodiment, the term purine or pyrimidine base includes, but isnot limited to, adenine, N⁶-alkylpurines, N⁶-acylpurines (wherein acylis C(O)(alkyl, aryl, alkylaryl, or arylalkyl), N⁶-benzylpurine,N⁶-halopurine, N⁶-vinylpurine, N⁶-acetylenic purine, N⁶-acyl purine,N⁶-hydroxyalkyl purine, N⁶-thioalkyl purine, N²-alkylpurines,N²-alkyl-6-thiopurines, thymine, cytosine, 5-fluorocytosine,5-methylcytosine, 6-azapyrimidine, including 6-azacytosine, 2- and/or4-mercaptopyrmidine, uracil, 5-halouracil, including 5-fluorouracil,C⁵-alkylpyrimidines, C⁵-benzylpyrimidines, C⁵-halopyrimidines,C⁵-vinylpyrimidine, C⁵-acetylenic pyrimidine, C⁵-acyl pyrimidine,C⁵-hydroxyalkyl purine, C⁵-amidopyrimidine, C⁵-cyanopyrimidine,C⁵-nitropyrimidine, C⁵-aminopyrimidine, N²-alkylpurines,N²-alkyl-6-thiopurines, 5-azacytidinyl, 5-azauracilyl,triazolopyridinyl, imidazolopyridinyl, pyrrolopyrimidinyl, andpyrazolo-pyrimidinyl. Purine bases include, but are not limited to,guanine, adenine, hypoxanthine, 2,6-diaminopurine, and 6-chloropurine.Functional oxygen and nitrogen groups on the base can be protected asnecessary or desired. Suitable protecting groups are well known to thoseskilled in the art, and include trimethylsilyl, trimethylhexylsilyl,t-butyldimethylsilyl and t-butyldiphenylsilyl, trityl, alkyl groups, andacyl groups such as acetyl and propionyl, methanesulfonyl, andp-toluenesulfonyl. Alternatively, the purine or pyrimidine base canoptionally be substituted such that it forms a viable prodrug, which canbe cleaved in vivo. Examples of appropriate substituents include acylmoiety, an amine or cyclopropyl (e.g., 2-amino, 2,6-diamino orcyclopropyl guanosine).

The term acyl refers to a carboxylic acid ester in which thenon-carbonyl moiety of the ester group is selected from straight,branched, or cyclic alkyl or lower alkyl (i.e., C₁-C₄), alkoxyalkylincluding methoxymethyl, aralkyl including benzyl, aryloxyalkyl such asphenoxymethyl, aryl including phenyl optionally substituted withhalogen, C₁ to C₄ alkyl or C₁ to C₄ alkoxy, sulfonate esters such asalkyl or aralkyl sulphonyl including methanesulfonyl, the mono, di ortriphosphate ester, trityl or monomethoxytrityl, substituted benzyl,trialkylsilyl (e.g. dimethyl-t-butylsilyl), or diphenylmethylsilyl. Arylgroups in the esters optimally comprise a phenyl group. The term “loweracyl” refers to an acyl group in which the non-carbonyl moiety is loweralkyl (i.e., C1-C₄).

The term “amino acid” or “amino acid residue” refers to a D- orL-natural or non-naturally occurring amino acid. Representative aminoacids alanine, β-alanine, arginine, asparagine, aspartic acid, cysteine,cystine, glutamic acid, glutamine, glycine, phenylalanine, histidine,isoleucine, lysine, leucine, methionine, proline, serine, threonine,valine, tryptophan, or tyrosine, among others.

The term “oxygen-protecting group” as used herein refers to a moietythat is covalently attached to oxygen and which can be removed, andtypically replaced with hydrogen, when appropriate. For example, anoxygen-protecting group may be a group that is removed in vivo afteradministration to a host, in vitro by a cell, or it may be removedduring a manufacturing process.

Phosphate ester refers to mono, di and tri phosphates unless otherwiseindicated.

The term “phosphoamidate,” phosphoramidate,” or “phosphoroamidate” is amoiety that has a phosphorus bound to three oxygen groups and an amine(which may optionally be substituted). The typical structure is—P(═O)(OR¹⁰⁰)(OR¹¹⁰)NR¹²⁰R¹³⁰, where R¹⁰⁰, R¹¹⁰, R¹²⁰, and R¹³⁰ can be Hor desired organic substituents. Suitable phosphoramidates useful in thepresent invention are described by Madela, Karolina and McGuigan in2012, “Progress in the development of anti-hepatitis C virus nucleosideand nucleotide prodrugs”, Future Medicinal Chemistry 4(5), pages 625-65010:1021/jm300074y. Additional phosphoramidates useful in the presentinvention are described in U.S. Pat. Nos. 7,964,580; 8,071,568;8,148,349; 7,879,815; 7,902,202; 7,547, 704; 7,951,789; 8,324,179; EP2120565; EP 1143995; 6,455,513; and 8,334,270. Other phosphoramidatesare described in the nucleoside patents described in the Background ofthe Invention.

Phosphoramidate groups for use in the present invention include those ofthe structures:

Other phosphoramidates include those of the structure:

wherein:

-   R^(P1) is an optionally substituted linear, branched, or cyclic    alkyl group, or an optionally substituted aryl, heteroaryl or    heterocyclic group or a linked combination thereof; and-   R^(P2) is a —NR^(N1)R^(N2) group or a B′ group;    wherein:-   R^(N1) and R^(N2) are each independently H or a alkyl group, often a    C₁-C₆ alkyl group which may be optionally substituted with one, two    or three hydroxyl groups, and,-   B′ is a

-    group;    wherein:-   R⁸ is sidechain of an amino acid, for example a sidechain of an    amino acid (as otherwise described herein) often selected from the    group consisting of alanine, β-alanine, arginine, asparagine,    aspartic acid, cysteine, cystine, glutamic acid, glutamine, glycine,    phenylalanine, histidine, isoleucine, lysine, leucine, methionine,    proline, serine, threonine, valine, tryptophan, or tyrosine (often    R⁸ is derived from alanine, leucine, valine, isoleucine or    threonine), and,-   R″ is H or an optionally substituted C₁ to C₂₀ linear, branched, or    cyclic alkyl group, or an optionally substituted aryl, heteroaryl or    heterocyclic group as otherwise described herein.

Preferred R^(P1) groups include optionally substituted C₈-C₂₀ alkylgroups and optionally substituted phenyl, naphthyl, and monocyclicheteroaryl groups, especially those groups (particularly lipophilicgroups) which enhance bioavailability of the compounds in the skin ofthe patient and which exhibit reduced toxicity, enhanced therapeuticindex and enhanced pharmacokinetics (the compounds are metabolized andexcreted more slowly).

The term “D-configuration” as used in the context of the presentinvention refers to the principle configuration which mimics the naturalconfiguration of sugar moieties as opposed to the unnatural occurringnucleosides or “L” configuration. The term “β” or “β anomer” is usedwith reference to nucleoside analogs in which the nucleoside base isconfigured (disposed) above the plane of the carbocyclic moiety in thenucleoside analog.

The terms “coadminister” and “coadministration” or combination therapyare used to describe the administration of at least one of thespiro[2.4] compounds according to the present invention in combinationwith at least one other anti-Flaviviridae agent, often at least oneadditional anti-HCV agent, including other spiro[2.4]heptane anti-HCVagents which are disclosed herein. The timing of the coadministration isbest determined by the medical specialist treating the patient. It issometimes preferred that the agents be administered at the same time.Alternatively, the drugs selected for combination therapy may beadministered at different times to the patient. Of course, when morethan one viral or other infection or other condition is present, thepresent compounds may be combined with other agents to treat that otherinfection or condition as required.

The term host, as used herein, refers to a unicellular or multicellularorganism in which the virus can replicate, including cell lines andanimals, and typically a human. Alternatively, the host can be carryinga part of the flavivirus or pestivirus genome, whose replication orfunction can be altered by the compounds of the present invention. Theterm host specifically refers to infected cells, cells transfected withall or part of the Flaviviridae, for example, HCV, genome and animals,in particular, primates (including chimpanzees) and humans. In mostanimal applications of the present invention, the host is a humanpatient. Veterinary applications, in certain indications, however, areclearly anticipated by the present invention (such as chimpanzees). Anumber of the Flaviviridae viruses are specific with respect to the hostanimal that is infected, and in those instances the term host refers tothose animals, including humans infected or susceptible to infection bythat Flaviviridae. The host can be for example, bovine, equine, avian,canine, feline, etc.

III. METHODS OF TREATMENT OR PROPHYLAXIS

Treatment, as used herein, refers to the administration of an activecompound to a host that is infected with a Flaviviridae virus, forexample, hepatitis C. The term “prophylactic” or preventative, whenused, refers to the administration of an active compound to prevent orreduce the likelihood of an occurrence of the viral disorder. Thepresent invention includes both treatment and prophylactic orpreventative therapies. In one embodiment, the active compound isadministered to a host who has been exposed to and thus at risk ofinfection by a Flaviviridae, for example, a hepatitis C infection.

The invention is directed to a method of treatment or prophylaxis of aFlaviviridae viral infection in a host in need thereof, includinghepatitis C virus, Yellow Fever virus, Dengue virus, JapaneseEncephalitis, and West Nile viruses, especially HCV, including drugresistant and multidrug resistant forms of HCV and related diseasestates, conditions, or complications of an HCV infection, includingcirrhosis and related hepatotoxicities, as well as other conditions thatare secondary to a Flaviviridae infection, such as weakness, loss ofappetite, weight loss, breast enlargement (especially in men), rash(especially on the palms), difficulty with clotting of blood,spider-like blood vessels on the skin, confusion, coma (encephalopathy),buildup of fluid in the abdominal cavity (ascites), esophageal varices,portal hypertension, kidney failure, enlarged spleen, decrease in bloodcells, anemia, thrombocytopenia, jaundice, and hepatocellular cancer,among others. The method comprises administering to a host in needthereof of an effective amount of at least one spiro[2.4]heptane asdescribed herein, optionally in combination with at least one additionalbioactive agent, for example, an additional anti-HCV oranti-Flaviviridae and/or anticancer agent, further in combination with apharmaceutically acceptable carrier additive and/or excipient.

In yet another aspect, the present invention is a method for preventionor prophylaxis of a Flaviviridae infection, such as an HCV infection ora disease state or related or follow-on disease state, condition orcomplication of a Flaviviridae, including an HCV, infection includingcirrhosis and related hepatotoxicities, weakness, loss of appetite,weight loss, breast enlargement (especially in men), rash (especially onthe palms), difficulty with clotting of blood, spider-like blood vesselson the skin, confusion, coma (encephalopathy), buildup of fluid in theabdominal cavity (ascites), esophageal varices, portal hypertension,kidney failure, enlarged spleen, decrease in blood cells, anemia,thrombocytopenia, jaundice, and hepatocellular (liver) cancer, amongothers, said method comprising administering to a patient at risk withan effective amount of at least one compound according to the presentinvention as described above in combination with a pharmaceuticallyacceptable carrier, additive, or excipient, optionally in combinationwith another anti-HCV agent. In another embodiment, the active compoundsof the invention can be administered to a patient after ahepatitis-related liver transplantation to protect the new organ.

The spiro[2.4]heptane can be administered if desired as any salt orprodrug that upon administration to the recipient is capable ofproviding directly or indirectly the parent compound, or that exhibitsactivity itself. Nonlimiting examples are the pharmaceuticallyacceptable salts and a compound, which has been modified at a functiongroup, such as a hydroxyl or amine function, to modify the biologicalactivity, pharmacokinetics, half-life, controlled delivery,lipophilicity, absorption kinetics, ease of phosphorylation to theactive 5′-triphosphate or efficiency of delivery using a desired routeof administration, of the compound. Methods to modify the properties ofan active compound to achieve target properties are known to those ofskill in the art or can easily be assessed by standard methods, forexample, acylation, phosphorylation, phosphoamidation, phosphonation,alkylation, pegylation, or selecting an R¹ or B that is metabolized to adesired R¹ or B.

IV. PHARMACEUTICAL COMPOSITIONS

In an aspect of the invention, pharmaceutical compositions according tothe present invention comprise an anti-Flaviviridae (especiallyincluding an anti-HCV) effective amount of at least one of thespiro[2.4]compounds described herein, optionally in combination with apharmaceutically acceptable carrier, additive, or excipient, furtheroptionally in combination with at least one other anti-viral, such as ananti-HCV agent.

The invention includes pharmaceutical compositions that include aneffective amount to treat a Flaviviridae infection, for example, ahepatitis C infection, of one of the spiro[2.4]heptane compounds of thepresent invention or its salt or prodrug, in a pharmaceuticallyacceptable carrier or excipient. In an alternative embodiment, theinvention includes pharmaceutical compositions that include an effectiveamount to prevent a Flaviviridae infection, for example, a hepatitis Cinfection, of one of the spiro[2.4]heptane compounds of the presentinvention or its salt or prodrug, in a pharmaceutically acceptablecarrier or excipient.

One of ordinary skill in the art will recognize that a therapeuticallyeffective amount will vary with the infection or condition to betreated, its severity, the treatment regimen to be employed, thepharmacokinetics of the agent used, as well as the patient or subject(animal or human) to be treated, and such therapeutic amount can bedetermined by the attending physician or specialist.

The spiro[2.4]heptane compound according to the present invention can beformulated in admixture with a pharmaceutically acceptable carrier. Ingeneral, it is preferable to administer the pharmaceutical compositionin orally-administrable form, but certain formulations may beadministered via a parenteral, intravenous, intramuscular, topical,transdermal, buccal, subcutaneous, suppository, or other route,including intranasal spray. Intravenous and intramuscular formulationsare often administered in sterile saline. One of ordinary skill in theart may modify the formulations to render them more soluble in water orother vehicle, for example, may be easily accomplished by minormodifications (salt formulation, esterification, etc.) which are wellwithin the ordinary skill in the art. It is also well within theroutineer's skill to modify the route of administration and dosageregimen of a particular compound in order to manage the pharmacokineticsof the present compounds for maximum beneficial effect in patients.

In certain pharmaceutical dosage forms, the pro-drug form of thecompounds, especially including acylated (acetylated or other), andether (alkyl and related) derivatives, phosphate esters,phosphoramidates, and various salt forms of the present compounds, arepreferred. One of ordinary skill in the art will recognize how toreadily modify the present compounds to pro-drug forms to facilitatedelivery of active compounds to a targeted site within the host organismor patient. The routineer also will take advantage of favorablepharmacokinetic parameters of the pro-drug forms, where applicable, indelivering the present compounds to a targeted site within the hostorganism or patient to maximize the intended effect of the compound.

The amount of compound included within therapeutically activeformulations according to the present invention is an effective amountfor treating the Flaviviridae infection or condition, for example an HCVinfection, reducing the likelihood of a HCV infection or the inhibition,reduction, and/or abolition of HCV or its secondary effects, includingdisease states, conditions, and/or complications which occur secondaryto HCV. In general, a therapeutically effective amount of the presentcompound in pharmaceutical dosage form usually ranges from about 0.001mg/kg to about 100 mg/kg per day or more, more often, slightly less thanabout 0.1 mg/kg to more than about 25 mg/kg per day of the patient orconsiderably more, depending upon the compound used, the condition orinfection treated and the route of administration. The active nucleosidecompound according to the present invention is often administered inamounts ranging from about 0.1 mg/kg to about 15 mg/kg per day of thepatient, depending upon the pharmacokinetics of the agent in thepatient. This dosage range generally produces effective blood levelconcentrations of active compound which may range from about 0.001 toabout 100, about 0.05 to about 100 micrograms/cc of blood in thepatient.

Often, to treat, prevent or delay the onset of these infections and/orto reduce the likelihood of a Flaviviridae infection, for example, anHCV infection, or a secondary disease state, condition or complicationof HCV, the compositions will be administered in oral dosage form inamounts ranging from about 250 micrograms up to about 500 mg or more atleast once a day, for example, at least 25, 50, 100, 150, 250 or 500milligrams, up to four times a day. The present compounds are oftenadministered orally, but may be administered parenterally, topically, orin suppository form, as well as intranasally, as a nasal spray or asotherwise described herein.

In the case of the co-administration of the present compounds incombination with another anti-HCV or Flaviviridae compound as otherwisedescribed herein, the amount of the compound according to the presentinvention to be administered ranges from about 0.01 mg/kg of the patientto about 500 mg/kg. or more of the patient or considerably more,depending upon the second agent to be co-administered and its potencyagainst the virus, the condition of the patient and severity of thedisease or infection to be treated and the route of administration. Theother anti-HCV or anti-Flaviviridae agent may for example beadministered in amounts ranging from about 0.01 mg/kg to about 500mg/kg. In certain preferred embodiments, these compounds may be oftenadministered in an amount ranging from about 0.5 mg/kg to about 50 mg/kgor more (usually up to about 100 mg/kg), generally depending upon thepharmacokinetics of the two agents in the patient. These dosage rangesgenerally produce effective blood level concentrations of activecompound in the patient.

For purposes of the present invention, a prophylactically or preventiveeffective amount of the compositions according to the present inventionfalls within the same concentration range as set forth above fortherapeutically effective amount and is usually the same as atherapeutically effective amount.

Administration of the active compound may range from continuous(intravenous drip) to several oral or intranasal administrations per day(for example, Q.I.D.) or transdermal administration and may includeoral, topical, parenteral, intramuscular, intravenous, sub-cutaneous,transdermal (which may include a penetration enhancement agent), buccal,and suppository administration, among other routes of administration.Enteric coated oral tablets may also be used to enhance bioavailabilityof the compounds from an oral route of administration. The mosteffective dosage form will depend upon thebioavailability/pharmacokinetics of the particular agent chosen as wellas the severity of disease in the patient. Oral dosage forms areparticularly preferred, because of ease of administration andprospective favorable patient compliance.

To prepare the pharmaceutical compositions according to the presentinvention, a therapeutically effective amount of one or more of thecompounds according to the present invention is often intimately admixedwith a pharmaceutically acceptable carrier according to conventionalpharmaceutical compounding techniques to produce a dose. A carrier maytake a wide variety of forms depending on the form of preparationdesired for administration, e.g., oral or parenteral. In preparingpharmaceutical compositions in oral dosage form, any of the usualpharmaceutical media may be used. Thus, for liquid oral preparationssuch as suspensions, elixirs, and solutions, suitable carriers andadditives including water, glycols, oils, alcohols, flavoring agents,preservatives, coloring agents, and the like may be used. For solid oralpreparations such as powders, tablets, capsules, and for solidpreparations such as suppositories, suitable carriers and additivesincluding starches, sugar carriers, such as dextrose, manifold, lactose,and related carriers, diluents, granulating agents, lubricants, binders,disintegrating agents, and the like may be used. If desired, the tabletsor capsules may be enteric-coated or sustained release by standardtechniques. The use of these dosage forms may significantly enhance thebioavailability of the compounds in the patient.

For parenteral formulations, the carrier will usually comprise sterilewater or aqueous sodium chloride solution, though other ingredients,including those which aid dispersion, also may be included. Of course,where sterile water is to be used and maintained as sterile, thecompositions and carriers must also be sterilized. Injectablesuspensions may also be prepared, in which case appropriate liquidcarriers, suspending agents, and the like may be employed.

Liposomal suspensions (including liposomes targeted to viral antigens)may also be prepared by conventional methods to produce pharmaceuticallyacceptable carriers. This may be appropriate for the delivery of freenucleosides, acyl/alkyl nucleosides or phosphate ester pro-drug forms ofthe nucleoside compounds according to the present invention.

In particularly preferred embodiments according to the presentinvention, the compounds and compositions are used to treat, prevent ordelay a HCV infection or a secondary disease state, condition orcomplication of HCV.

IV. COMBINATION AND ALTERNATION THERAPY

It is well recognized that drug-resistant variants of viruses can emergeafter prolonged treatment with an antiviral agent. Drug resistance mosttypically occurs by mutation of a gene that encodes for an enzyme usedin viral replication. The efficacy of a drug against a Flaviviridaeinfection, including an HCV infection, can be prolonged, augmented, orrestored by administering the compound in combination or alternationwith another, and perhaps even two or three other, antiviral compoundsthat induce a different mutation or act through a different pathway,from that of the principle drug. Alternatively, the pharmacokinetics,bio distribution, half-life, or other parameter of the drug can bealtered by such combination therapy (which may include alternationtherapy if considered concerted). Since the disclosed spiro[2.4]heptanesare NS5B polymerase inhibitors, it may be useful to administer thecompound to a host in combination with, for example a:

(1) Protease inhibitor, such as an NS3/4A protease inhibitor;

(2) NS5A inhibitor;

(3) Another NS5B polymerase inhibitor;

(4) NS5B non-substrate inhibitor;

(5) Interferon alfa-2a, which may be pegylated or otherwise modified,and/or ribavirin;

(6) Non-substrate-based inhibitor;

(7) Helicase inhibitor;

(8) Antisense oligodeoxynucleotide (S-ODN);

(9) Aptamer;

(10) Nuclease-resistant ribozyme;

(11) iRNA, including microRNA and SiRNA;

(12) Antibody, partial antibody or domain antibody to the virus, or

(13) Viral antigen or partial antigen that induces a host antibodyresponse.

Non limiting examples of anti-HCV agents that can be administered incombination with the spiro[2.4]heptanes of the invention are:

-   -   (i) protease inhibitors such as telaprevir (Incivek), boceprevir        (Victrelis), ACH-2684; AZD-7295; BMS-791325; danoprevir;        Filibuvir; GS-9256; GS-9451; MK-5172; Setrobuvir; Sovaprevir;        Tegobuvir; VX-135; VX-222 and ALS-220;    -   (ii) NS5A inhibitor such as ACH-2928 and ACH-3102;    -   (iii) NS5B inhibitors such as ACH-3102; AZD-7295; Clemizole;        ITX-5061; PPI-461; PPI-688; IDX-719, PSI-7977 and mericitabine;    -   (iv) NS5B inhibitors such as MBX-700; and,    -   (v) Antibody such as GS-6624.

If the spiro[2.4]heptane is administered to treat advanced hepatitis Cleading to liver cancer or cirrhosis, in one embodiment, the compoundcan be administered in combination or alternation with another drug thatis typically used to treat hepatocellular carcinoma (HCC), for example,as described by Andrew Zhu in “New Agents on the Horizon inHepatocellular Carcinoma” Therapeutic Advances in Medical Oncology, V5(1), January 2013, 41-50. Examples of suitable compounds forcombination therapy where the host has or is at risk of HCC includeanti-angiogenic agents, sunitinib, brivanib, linifanib, ramcirumab,bavcizumab, cediranib, pazopanib, TSU-68, lenvatinib, antibodies againstEGFR, mTor inhibitors, MEK inhibitors, and histone decetylaceinhibitors.

V. PROCESS OF PREPARATION OF SPIRO[2.4]HEPTANES OF THE INVENTION

General methods for providing the compounds of the present invention areknown in the art or described herein. Examples of processes to preparethe described compounds are set out in detail in FIGS. 2-11 (withdetails of reagents provided in the Brief Description of the Figures)which can be used as desired or with minor modification within theroutineer's skill. Further exemplication is provided below in thedetailed synthetic examples.

The following abbreviations are used in the synthetic schemes.

(Boc)₂O: Di-tert-butyl dicarbonate;

DMAP: 4-Dimethylaminopyridine;

THF: Tetrahydrofuran (THF), anhydrous;

OsO₄: Osmium tetraoxide;

NMO: N-Methylmorpholine N-oxide;

BzCl: Benzoyl Chloride;

NaBH₄: Sodium borohydride;

HCl: Hydrochloric Acid;

NaNO₂: Sodium Nitrite;

CH₃COOH: Acetic Acid;

NaOMe: Sodium Methoxide;

PTSA: p-toluene sulphonic acid;

TBDMSCl₂: 1,3-Dichloro-1,1,3,3-tetraisopropyldisiloxane;

DCM: Methylene chloride (CH₂Cl₂), anhydrous;

m-CPBA: m-Chloro perbenzoic acid;

n-BuLi: n-Butyl Lithium;

CeCl₃.7H₂O: Cerium(III)chloride heptahydrate;

MeI₂: Diido methane;

DIAD: Diisopropyl azodicarboxlate;

TPP: Triphenylphosphine;

TFA: Trifluoro acetic acid;

TBAF: Tetrabutylammonium fluoride;

NMI: N-methyl Imidazole;

DPPA: Diphenylphosphoryl azide;

NaH: Sodium hydride;

EtOAc: Ethyl acetate;

Silica gel (230 to 400 mesh, Sorbent);

Na₂SO₄: Sodium Sulphate (anhydrous);

DMF: N′N Dimethyl formamide, androus;

NH₄OH: Ammoinum hydroxide;

EtOH: Ethanol;

MeOH: Methanol;

DAST: Diethylaminosulfur trifluoride;

NaHCO₃: Sodium bicarbonate;

BnCl: Benzyl Chloride;

NH₃: Ammonia;

PCC: Pyridinium chlorochromate;

CH₃Li: Methyl lithium; and,

CH₃MgBr: Methyl magnesium bromide.

Examples General Methods

Melting points were determined on a Mel-temp II laboratory device andare uncorrected. Nuclear magnetic spectra were recorded on VarianMercury 400 spectrometer at 400 MHz for ¹H NMR and 100 MHz for ¹³C NMRor Varian Inova 500 spectrometer at 500 MHz for ¹H NMR and 125 MHz for¹³C NMR with tetramethylsilane as an internal standard. Chemical shifts(δ) are quoted as s (singlet), bs (broad singlet), d (doublet), t(triplet), q (quartet), m (multiplet). U.V spectra were recorded on aBeckman DU-650 spectrophotometer. Optical rotations were measured onJASCO DIP-370 digital polarimeter. High resolution mass spectra wererecorded on a Micromass Autospec high-resolution mass spectrometer.Elemental analyses were performed by Atlantic Microlabs Inc. Norcross,Ga. TLC was performed on Uniplates (Silica Gel) purchased from AnaltechCo.

Detailed Synthetic Protocols for FIG. 2 [(±)-tert-butyl3-oxo-2-azabicyclo(2.2.1)hept-5-ene-2-carboxylate] (2)

A solution of di-tert-butyl dicarbonate (110.0 g, 504.5 mmol) intetrahydrofuran (50 ml) was added slowly to a suspension of racemic 1(50.0 g, 403.2 mmol), and 4-dimethylaminopyridine (0.5 g, 4.0 mmol) intetrahydrofuran (150 ml). The brown, hazy solution was stirred at 20° C.until reaction was complete. The solution was concentrated in vacuo togive brown foam. Recrystallisation twice from cyclohexane afforded theproduct 2 (racemic) as pale pink crystals (80.8 g, 80%); mp 70.5-71.5°C.; ¹H NMR (CDCl3): δ 1.5 (s, 5H), 2.15 (d, J=8.5 Hz, 1H), 2.35 (d,J=8.5 Hz, 1H), 3.39 (s, 1H), 4.96 (s, 1H), 6.66 (m, 1H), 6.89 (dd, J=5.6& 2.1 Hz, 1H); MS: (M+H)⁺ 210.

(−)-[(1R,4S)-tert-butyl3-oxo-2-azabicyclo(2.2.1)hept-5-ene-2-carboxylate] (3)

Savinase (15 ml, 16 L) was added to a solution (500 ml) containing 10 g(47.8 mmol) of (±) 2 in 50% tetrahydrofuran:50% phosphate buffer (50 mM,pH 8.0) at 30° C. The reaction was monitored by TLC for up to 2 days.Upon completion of the reaction (51% conversion), the pH of theclarified solution was raised to 9 with a sodium bicarbonate solution.This was then extracted with cyclohexane (200 mL×2). The combinedorganic phase was back extracted with 100 ml of sodium bicarbonatesolution and subsequently washed with 100 ml of brine. Evaporation anddrying yielded brown crude. The obtain crude was purified by the columnchromatography eluent 20% EtOAc/hexane gave free flowing white solid(−)-3 (4.2 g, 84%) which was identified by 1H NMR and by with anauthentic enantiomerically pure standard (optical rotation of standard[α]²⁴ _(D)−194° (c 2.0, CHCl₃). The enantiomeric excess was better than99% as analyzed by the optical rotation. Mp 88.6° C.; [α]²⁴ _(D)−193° (c2.0, CHCl₃); ¹H NMR (CDCl₃): δ 1.5 (s, 5H), 2.15 (d, J=8.5 Hz, 1H), 2.35(d, J=8.5 Hz, 1H), 3.39 (s, 1H), 4.96 (s, 1H), 6.66 (m, 1H), 6.89 (dd,J=5.6 & 2.1 Hz 1H).

(−)-(1R,4S,5R,6S)-tert-butyl5,6-dihydroxy-3-oxo-2-azabicyclo[2.2.1]heptane-2-carbo-late(4)

To a solution of tert-butyl 3-oxo-2-azabicyclo(2.2.1)hept-5-ene-2-carboxylate 3 (50.0 g, 239.2 mmol) in acetone (200 mL),N-Methylmorpholine N-oxide (55.9 g, 477.7 mmol) was added at 0° C. withstirring followed by a solution of OsO₄ (121 mg, 0.476 mmol) intert-butyl alcohol (2.5 mL), and the mixture was stirred at roomtemperature for 2 hr. Solvents were evaporated in vacuo, and the residuewas purified by flash column chromatography on silica gel using 30%EtOH/hexane as the eluent to give a white solid (35 g, 70%). [α]²⁴_(D)−28.19 (c 1.0 CHCl₃); ¹H-NMR (500 MHz, CDCl₃): δ 4.33 (m, 1H), 4.24(m, 1H), 4.09 (m, 1H), 3.92 (brs, 1H), 3.76 (brs, 1H), 2.80 (m, 1H),2.10 (d, J=10.5 Hz, 1H), 1.99 (d, J=10.5 Hz, 1H), 1.52 (s, 9H); HR-MSCalcd. For (C₁₁H₁₇NO₅+H)⁺ 244.1107, found 244.1321.

(−)-(1R,2S,3R,5R)-3-((tert-butoxycarbonyl)amino)-5-(hydroxymethyl)cyclopentane-1,2-diyldibenzoate (5)

Benzoyl chloride (11.9 mL, 102.8 mmol) was added into a solution of diol4 (10.0 g, 41.1 mmol) and DMAP (7.5 g, 61.4 mmol) in anhydrousdichloromethane (150 ml) at 0° C. The mixture was then stirred for 1 hr,quenched with water and the mixture was extracted with DCM (50 mL×2).The combined organic layers were washed with brine (150 mL) dried overNa₂SO₄. The solvent was removed and the residue was purified by silicagel column chromatography (8% EtOAc/hexane) to give benzoylatedintermediate as white solid. [α]²⁴ _(D)−43.40; ¹H-NMR (500 MHz, CDCl₃):δ 7.82 (m, 4H), 7.50 (m, 2H), 7.25 (m, 4H), 5.59 (d, J=5.5 Hz, 1H), 5.48(d, J=5.5 Hz, 1H), 4.70 (m, 1H), 3.13 (m, 1H), 2.43 (d, J=10.5 Hz, 1H),2.76 (d, J=10.5 Hz, 1H), 1.57 (s, 9H). The bezoylated intermediated(12.0 g, 26.6 mmol) dissolved in the Methanol and added sodiumborohydried (2.7 g, 66.5 mmol) at 0° C. The reaction was allowed to warmto room temperature. After 1.5 hr mixture was quenched with 1 N HCl andconcentrated in vacuo. The aqueous layer was extracted with ethylacetate (100 mL×2) and combine organic layers were washed with waterdried over Na₂SO₄ and concentrated in reduced pressure. The residue waspurified by silica gel column chromatography (50% DCM/hexane) to givecompound 5 (8.5 g, 95%) as off white solid. mp 78-79° C.; ¹H-NMR (500MHz, CDCl₃): δ 7.97 (m, 4H), 7.54 (m, 2H), 7.38 (m, 4H), 5.56 (m, 1H),5.38 (s, 1H), 5.30 (m, 1H), 4.52 (m, 1H), 3.87 (m, 1H), 3.72 (m, 1H),2.52 (m, 2H), 1.43 (s, 9H); HR-MS Calcd. For (C₂₅H₂₉NO₇+H)⁺ 456.1944,found 456.2017.

(−)-(1R,2S,3R,5R)-3-amino-5-(hydroxymethyl)cyclopentane-1,2-diyldibenzoate hydrochloride (6)

2 N solution of HCl in ether (15 ml) was added in stirring solution ofcompound 5 (10.0 g, 21.9 mmol) in methanol at 0° C. The mixture wasallowed to warm to room temperature gradually and continue stirred for 2hr. Solvent was evaporated under reduced pressure, and the residue wastreated with anhydrous ether (120 mL) to precipitate the product 6. Theprecipitated product was washed with ether (50 mL×2) afforded the titledcompound as white solid. [α]^(D) ₂₅−28.19°; ¹H NMR (500 MHz, DMSO-d₆): δ8.40 (bs, 2H, D₂O exchange, NH₂), 7.88 (m, 4H), 7.64 (m, 2H), 7.45 (m,4H), 5.48 (m, 2H), 5.07 (m, 1H), 3.96 (m, 1H), 3.61 (m, 1H), 3.52 (m,1H), 2.47 and 2.39 (m, 1H), 1.63 (m, 1H); HR-MS Calcd. For (C₂₀H₂₁NO₅)⁺355.1420, found 335.1293.

(+)-(1R,2S,5R)-5-(hydroxymethyl)cyclopent-3-ene-1,2-diyl dibenzoate (7)

To a well stirred solution of(−)-(1R,2S,3R,5R)-3-amino-5-(hydroxymethyl)cyclopentane-1,2-diyldibenzoate hydrochloride (6) (10.0 g, 25.5 mmol) in mixture ofacetonitrile/water (1:1) was added sodium nitrite (8.8 g, 127.8 mmol) byportion wise at 0° C. After 15 minutes 50% aqueous acetic acid solutionwas added drop wise over a period of 0.5 hr and the mixture wasvigorously stirred for 2 hr. The organic solvent was removed underreduced pressure and the rest of mixture was quenched with water. Theaqueous phase was extracted with EtOAc (50 mL×3). The combined organiclayers were dried over Na₂SO₄, filtered and the solvent was removedunder reduced pressure. The residue was purified by flash silica gelcolumn chromatography (20% EtOAc/hexane) to give compound 7. [α]²⁴_(D)−156° (c 1.0, CHCl₃); ¹H NMR (500 MHz, DMSO-d₆): δ 8.05 (m, 2H),7.89 (m, 2H), 7.52 (m, 2H), 7.38 (m, 2H), 7.28 (m, 2H), 6.11 (m, 3H),5.54 (m, 1H), 3.87-3.82 (m, 2H), 3.27 (m, 1H), 2.29 (m, 1H). HR-MSCalcd. For (C₂₅H₂₉NO₇+H)⁺ 339.1154, found 339.1286.

(+)-(1R,2S,5R)-5-(hydroxymethyl)cyclopent-3-ene-1,2-diol (8)

To a stirred solution of(1R,2S,5R)-5-(hydroxymethyl)cyclopent-3-ene-1,2-diyl dibenzoate (7) (7.5g, 22.1 mmol) in methanol at room temperature under N₂ atmosphere wasadded drop wise sodium methoxide (25% by wt in methanol) (14.3 mL, 77.66mmol) over a period of 20 minutes. The mixture was stirred at roomtemperature for 2 hr and quenched drop wise with 1N HCl solution to thepH neutral. The solvent was removed under reduced pressure and theobtained residue was purified by silica gel column chromatography (5%MeOH/DCM) to give triol 8 (2 g, 71%) as an oil; [α]²⁴ _(D)+254.04° (c1.0, MeOH); ¹H NMR (500 MHz, CD₃OD) δ 2.78 (d, J=5.0 Hz, 1H), 3.73 (dd,J=5.0, 11.0 Hz, 1H), 3.55 (dd, J=6.5, 10.5 Hz, 1H), 3.93 (t, 1H), 4.50(t, 1H), 5.88-5.87 (m, 1H), 5.97 (d, J=6.0 Hz, 1H); ¹³C NMR (125 MHz,CD₃OD) δ 53.7, 62.2, 73.2, 74.5, 132.0, 135.0; HR-MS Calcd. For(C₆H₁₀O₃−H)⁺ 129.0630, found 129.0553.

(+)-tert-butyl(((3aR,4R,6aS)-2,2-dimethyl-4,6a-dihydro-3aH-cyclopenta[d][1,3]dioxol-4-yl)methoxy)dimethylsilane(9)

To a stirred mixture of compound (8) (4.0 g, 30.7 mmol) in dry acetone(30 mL), cooled at 0° C. was added PTSA (0.18 g, 0.92 mmol) and2,2-dimethoxy propane drop wise (4.5 mL, 36.9 mmol). The mixture wasstirred at room temperature for 2 hr, quenched with solid NaHCO₃ (0.15g, 1.84 mmol) and the suspension was filtered through celite pad. Thecelite bed was washed with acetone (20 mL) and filtrate was concentratedunder vacuum. The crude acetonide was purified by silica gel columnchromatography (10% EtOAc/Hexane) to give acetonide intermediate (4.0 g,76%) as an oil. ¹H NMR (500 MHz, CDCl₃) δ 5.94-5.93 (m, 1H), 5.78-5.76(m, 1H), 5.16-5.15 (m, 1H), 4.61-4.60 (m, 1H), 3.76-3.73 (m, 1H),3.58-3.55 (m, 1H), 3.00-2.99 (m, 1H), 1.95 (br, OH), 1.43 (s, 3H), 1.36(s, 3H). A stirred solution of acetonide intermediate (4.0 g, 23.5 mmol)and imidazole (4.8 g, 70.5 mmol) in dry dichloromethane (50 mL) wascooled at 0° C. TBDMSCl (7.09 g, 47.0 mmol) was added in mixture andcontinue stirred overnight at room temperature under nitrogenatmosphere. The mixture was diluted with 100 mL dichloromethane andwashed with a saturated solution of NH₄Cl (50 ml×2), finally with water(50 ml). The organic layer was dried over Na₂SO₄ and concentrated underreduced pressure. The residue was purified by silica gel columnchromatography to give 9 as an oil (5.3 g, 80%); [α]²⁴ _(D)+86.39° (c0.2, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ 5.83-5.81 (m, 1H), 5.73-5.71 (m,1H), 5.09-5.07 (m, 1H), 4.51-4.49 (m, 1H), 3.67-3.65 (m, 1H), 3.55-3.52(m, 1H), 2.99-2.91 (m, 1H), 1.39 (s, 3H), 1.33 (s, 3H), 0.89-0.85 (m,9H), 0.082-0.014 (m, 6H). HR-MS Calcd. For (C₂₆H₃₂O₅Si+H)⁺ 453.2019,found 453.2123.

(+)-tert-butyl(((1aR,1bR,4aR,5S,5aR)-3,3-dimethyltetrahydro-1aH-oxireno[2′,3′:3,4]-cyclopenta[1,2-d][1,3]dioxol-5-yl)methoxy)dimethylsilane(10)

To a stirred solution of compound 9 (5.0 g, 17.5 mmol) indichloromethane (40 mL) at room temperature was added portion wisem-CPBA (13.6 g, 78.9 mmol). Mixture was stirred at room temperature for6 h, quenched with saturated NaHCO₃ solution and the mixture wasextracted with DCM (50 mL×2). The combined organic layers were washedwith brine (40 mL×2) dried over Na₂SO₄. The solvent was removed underreduced pressure and residue was purified by silica gel columnchromatography (3% EtOAc/Hexane) to give epoxide 10 (3.5 g, 66%) as anoil. [α]²⁴ _(D)+58.19° (c 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ4.54-4.52 (m, 1H), 3.91-3.90 (m, 1H), 3.73-3.69 (m, 1H), 3.59-3.55 (m,3H), 2.316-2.311 (m, 1H), 1.38 (s, 3H), 1.22 (s, 3H), 0.83-0.82 (m, 9H),0.006-0.000 (m, 6H); HR-MS Calcd. For (C₁₅H₂₈O₄Si+H)⁺ 301.1757, found301.1895.

(−)-(3aS,4R,6R,6aR)-6-(((tert-butyldimethylsilyl)oxy)methyl)-2,2-dimethyl-5-methylenetetrahydro-3aH-cyclopenta[d][1,3]dioxol-4-ol(11)

To a −10° C. suspension of trimethylsulfonium iodide (30 g, 149.5 mmol)in THF (150 mL) was added n-BuLi 2.5 M hexane solution (46.0 mL, 83.0mmol). After 30 min, epoxide (10) (5.0 g, 16.6 mmol) in THF (20 mL) wasintroduced and the reaction slowly allowed to warm to 0° C. over 1 h;the mixture was then stirred at ambient temperature for 2 hr. Thereaction was quenched with water and extracted with ethyl acetate (50mL×2). The combined organic layers were washed with brine, dried overNa₂SO₄, filtered, and concentrated under vacuum. The residues werepurified on silica gel column chromatography (10% EtOAc/Hexane) to giveallylic alcohol 11 (4 g, 80%) as an oil. [α]²² _(D)−20.35° (c 2.0,CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ 5.31 (s, 1H), 5.11 (s, 1H), 4.52 (d,J=6 Hz, 1H), 4.32-4.31 (m, 1H), 4.13-4.11 (m, 1H), 3.81-3.79 (m, 2H),3.62-3.60 (m, 1H), 3.91-3.90 (m, 1H), 2.62 (br, 1H), 1.30 (s, 3H), 1.20(s, 3H), 0.80 (m, 9H), 0.013-0.006 (m, 6H); ¹³C NMR (125 MHz, CDCl₃) δ157.9, 115.9, 92.6, 88.8, 84.1, 72.4, 59.0, 32.6, 31.5, 30.4, 24.0,0.05; HR-MS Calcd. For (C₁₆H₃₀O₄Si+H)⁺ 315.1913, found 315.1892.

(−)-(3aS,4S,6R,6aR)-6-(((tert-butyldimethylsilyl)oxy)methyl)-2,2-dimethyl-5-methylene-tetrahydro-3aH-cyclopenta[d][1,3]dioxol-4-ol(12)

To a stirred solution of allylic alcohol 11 (4 g, 12.7 mmol) was addeddess marline (8.1 g, 19.7 mmol) at 0° C. The mixture was warm to ambienttemperature and stirred for 1 hr. The mixture was passed through celitebed and obtained filtrate was concentrated under reduced pressure togive crude allylic ketone, which was proceeded as such in next stepwithout further purification. The crude allylic ketone (3.5 g, 11.1mmol) was dissolved in anhydrous methanol, cooled the solution at −78°C. Added CeCl₃.7H₂O (5.8 g, 15.6 mmol) at −78° C. and after 10 minutesstirring NaBH₄ (0.54 g, 14.5 mmol) was added at one portion. After 15min stirring at −78° C., the reaction mixture was allowed to 0° C. thensaturated NH₄Cl (30 mL) was added and the mixture was allowed to stirfor 1 hr. Solvent was removed under reduced temperature and pressure andthe residue was extracted with DCM (200 mL×2). The combined DCM extractswere washed with brine (40 mL×2), dried over anhydrous Na₂SO₄, filteredand concentrated under vacuum. The residue was purified by flash silicagel column chromatography (5% EtOAc/hexane) to give compound 12 (3.2 g,80%) as oil. [α]²² _(D)−96.878° (c 2.01, CHCl₃); ¹H NMR (500 MHz, CDCl₃)δ 5.26 (s, 1H), 5.10 (s, 1H), 4.52 (m, 2, 3-H's, 2H), 4.4 (m, 1H, 1-H′),3.71 (dd, J=4 & 10 Hz, 1H, 5-Ha), 3.53 (dd, J=4 & 10 Hz, 5-Hb, 1H), 2.57(br, 1H), 2.29 (d, J=10.5 Hz, D₂O exchange, OH), 1.38 (s, 3H), 1.30 (s,3H), 0.85 (m, 9H), 0.013-0.006 (m, 6H). ¹³C NMR (125 MHz, CDCl₃) 159.01,115.9, 115.4, 86.85, 84.85, 79.48, 71.63, 57.21, 32.13, 31.54, 30.33,23.83, 0.015; HR-MS Calcd. For (C₁₆H₃₀O₄Si+H)⁺ 315.1913, found 315.1987.

(−)-(3aR,4R,6S,6aS)-4-(((tert-butyldimethylsilyl)oxy)methyl)-2,2-dimethyltetrahydrospiro[cyclopenta[d][1,3]dioxole-5,1′-cyclopropan]-6-ol(13)

To a solution of 12 (3 g, 9.5 mmol) in anhydrous ether (50 mL) was addeddiethyl zinc (1.0 M solution in hexane, 24.2 mL, 28.6 mmol) followed bydiiodomethane (4.6 mL, 57.3 mmol) at 0° C. The reaction mixture wasallowed to room temperature and was refluxed for 8 hr. The reactionmixture was cooled to 0° C. and quenched with saturated NH₄Cl solution(20 mL) and extracted with ether (2×60 mL). The combined organic layerswere washed with water (30 mL), brine (30 mL), dried over Na₂SO₄ andconcentrated under reduced pressure. The residue was purified by columnchromatography (5% EtOAc/hexane) to afford 13 (3.0 g, 93%) as an oil.[α]²⁴ _(D)−86.03° (c 2.01, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ 4.55 (m,1H), 4.49 (m, 1H), 4.08 (m, 1H), 3.59 (dd, J=3.0 & 9.5 Hz), 3.50 (dd,J=4.5 & 10.5 Hz, 1H), 2.22 (d, J=10.5 Hz, D₂O exchange OH, 1H), 1.57 (m,1H), 1.44 (s, 3H), 1.31 (s, 3H), 0.84 (m, 10H), 0.43 (m, 1H), 0.32 (m,1H), 0.24 (1H), −0.06 (s, 6H). ¹³C NMR (125 MHz, CDCl₃) 159.01, 115.9,115.4, 86.85, 84.85, 79.48, 71.63, 57.21, 32.13, 31.54, 30.33, 29.2423.83, 7.14, 0.015; HR-MS Calcd. For (C₁₇H₃₂O₄Si)⁺ 328.2070, found328.2195.

(−)-(3aS,4R,6R,6aR)-6-(((tert-butyldimethylsilyl)oxy)methyl)-2,2-dimethyltetrahydrospiro[cyclopenta[d][1,3]dioxole-5,1′-cyclopropan]-4-amine(14)

Compound 13 (0.5 g, 1.52 mmol) and PPh₃ (0.8 g, 3.04 mmol) weredissolved in anhydrous THF (20 mL), diisopropylethylamine (0.5 mL, 3.04mmol) was added and the mixture cooled to 10° C. DIAD (0.62 mL, 3.04mmol) was then added slowly over 15 min at temperature 10° C. and thereaction mixture stirred for 10 min. DPPA (0.66 mL, 3.08 mmol) was thenadded drop wise over 10 min at 15° C., and the reaction mixture waswarmed to 25° C. over a period of 30 minute, stirred for addition 2 hr.Mixture was quenched with methanol concentrated on reduced pressure,residue was purified by the column chromatography (3% EtOAc/hexane) togive the azide intermediate as an oil. IR 2097 cm⁻¹; ¹H NMR (500 MHz,CDCl₃) δ 4.65 (d, J=8 Hz, 1H), 4.47 (d, J=7.5 Hz, 1H), 3.67-4.58 (m,1H), 1.80-1.77 (m, 1H), 1.48 (s, 3H), 1.31 (s, 3H), 1.20 (s, 3H),0.91-0.86 (m, 9H), 0.79-0.77 (m, 1H, cp), 0.72-0.0.69 (m, 2H, cp),0.68-0.65 (m, 1H, cp), 0.06-0.05 (m, 6H). A suspension of azidointermediate (0.4 g, 2.33 mmol) and 10% Pd/C (330 mg) in absolute EtOHwas shaken under 30 psi of H₂ at room temperature for 2 hr. Celite wasadded into the solution and the slurry was filtered through a celitepad. The volatile was removed in vacuo and the residue was purified bycolumn chromatography on silica gel (2% MeOH/DCM) to give 14 (0.86 g,95%) as an oil. ¹H NMR (500 MHz, CDCl₃): δ 4.58 (dd, J=1.5 & 6.0 Hz,1H), 4.29 (dd, J=1.0 & 6.0 Hz), 3.67 (m, 2H), 2.76 (m, 1H), 1.78 (m,1H), 1.49 (s, 3H), 1.31 (s, 3H), 0.90 (s, 9H), 0.68 (m, 1H), 0.60 (m,1H), 0.48 (m, 2H), 0.003 (s, 6H); ¹³C (125 MHz, CDCl3): δ 0.000, 7.31,21.022, 23.82, 30.22, 31.44, 32.33, 34.06, 60.07, 69.41, 70.23, 89.09,93.94, 115.65. HR-MS Calcd. For (C₁₇H₃₃NO₃Si)⁺ 328.2230, found 328.2568.

(−)-1-((3aR,4R,6R,6aS)-4-(((tert-butyldimethylsilyl)oxy)methyl)-2,2-dimethyltetrahydrospiro[cyclopenta[d][1,3]dioxole-5,1′-cyclopropan]-6-yl)pyrimidine-2,4(1H,3H)-dione(16)

To a suspension of silver cynate (0.81 g, 5.5 mmol) in anhydrous benzene(20 mL), β-methoxyacryloyl chloride (0.6 g, 5.4 mmol) was added. Themixture was heated under reflux for 30 minutes and cooled to roomtemperature. The supernatant solution was added into the solution ofamine 14 (0.7 g, 2.1 mmol) in anhydrous THF (30 mL) at −30° C. during 15minutes. The mixture was allowed to gradually warm up to roomtemperature and kept overnight. After removing the solvent in vacuo, theresidue was purified by column chromatography on silica gel (30%EtOAc/Hexane) to give crude 15 (0.6 g) as a yellow syrup which wasdirectly used for next step. Crude compound 15 (0.6 g) was dissolved in1,4-dioxane/ethanol (20 mL/20 mL) and treated with 28% solution ofammonium hydroxide (20 mL) in a steel bomb at 90-100° C. for 17 hr.After removing the solvent in vacuo, the residue was purified by columnchromatography on a silica gel (2% MeOH/DCM) to give 16 (0.36 g, 41%) asa pale yellow syrup. [α]²² _(D)−86.03 (c 2.01, CHCl₃); ¹H NMR (500 MHz,CDCl₃) δ 8.81 (brs, 1H, NH), 7.64 (d, J=8.0 Hz, 1H), 5.56 (d, J=8.0 Hz,1H), 4.68 (m, 1H), 4.47 (m, 2H), 3.54 (m, 2H), 2.08 (m, 1H), 1.50 (s,3H), 1.25 (s, 3H), 0.80 (m, 11H), 0.72 (m, 1H), 0.26 (m, 1H), 0.003 (s,6H); ¹³C (125 MHz, CDCl3): δ −5.43, 7.82, 16.47, 18.39, 24.48, 25.94,27.58, 52.13, 62.68, 82.28, 85.92, 101.74, 111.72, 143.46, 150.96,163.02; HR-MS Calcd. For (C₁₇H₃₂O₄Si)⁺ 328.2070, found 328.2295.

(−)-1-((4R,5S,6R,7R)-5,6-dihydroxy-7-(hydroxymethyl)spiro[2.4]heptan-4-yl)pyrimidine-2,4(1H,3H)-dione(17)

Compound 16 (0.2 g, 0.47 mmol) was dissolved in 20 mL of CF₃COOH/H₂O(2:1, v/v) and heated to 50° C. for 3 hr. The solvent was removed undervacuum and the residue was co-evaporated with ethanol (10 mL×3) undervacuum. The residue was purified by column chromatography on a silicagel (7% MeOH/CH₂Cl₂) to give 17 (100 mg, 79%) as white foam. mp 114-116°C.; [α]²⁴ _(D) 9.84° (c 0.26, MeOH); UV(MeOH) λ_(max) 265 nm (ε 11713,pH 2), 265 nm (ε 11887, pH 7), 264 nm (ε 9153, pH 11); ¹H NMR (500 MHz,CD₃OD-d₆) δ 7.50 (d, J=8.5 Hz, 1H), 5.68 (d, J=8.5 Hz, 1H), 4.77-4.73(m, 2H), 4.62 (d, J=3 Hz, 1H), 3.71 (dd, J=4.5 & 11.0 Hz, 1H), 3.62 (dd,J=5 & 11.0 Hz, 1H), 2.26 (m, 1H), 0.87 (m, 2H), 0.81 (m, 1H), 0.33 (m,1H); ¹³C NMR (125 MHz, CD₃OD) δ 165.1, 152.2, 146.3, 109.9, 74.3, 72.4,63.4, 51.1, 29.8, 28.7, 10.9; HR-MS Calcd. For (C₁₂H₁₆N₂O₅+H)⁺ 269.1059,found 269.1261.

General Procedure for Synthesis of Prodrug 18, 19, and 20

N-Methylimidazole (NMI, 5.0 mmol) was added to a stirring suspensioncompound 17 (1 mmol) in dry THF under argon atmosphere at −78° C. Theappropriate substituted chlorophenylphosphoryl-L-alaninate (3.0 mmol)dissolve in THF was added drop wise, slowly heated up to roomtemperature and continue stirred over night at room temperature.Volatiles were evaporated, and the residue was dissolved indichloromethane (DCM) and washed with 0.5 N HCl. The organic layer driedover Na₂SO₄ filtered, concentrated to dryness under reduced pressure,and the residue was purified by flash chromatography to give theprodrugs of compound 17 (18, 19 & 20).

(−)-(2R)-isopropyl2-(((((4R,5R,6S,7R)-7-(2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)-5,6-dihydroxyspiro[2.4]heptan-4-yl)methoxy)(phenoxy)phosphoryl)amino)propanoate(18)

¹H NMR (500 MHz, DMSO-d₆) δ 11.17 (bs, 1H, NH), 7.68 (d, J=6.8 Hz, 1H),7.34-7.15 (m, 5H), 5.00 (d, J=6 Hz, 1H), 4.74-4.78 (bs, 2H, —OH), 4.70(d, J=4 Hz, 1H), 4.68 (d, J=7.6 Hz, 1H), 4.21 (m, 1H); 4.11 (m, 2H),3.93-3.90 (m, 1H), 3.32-3.43 (m, 2H), 1.78-1.81 (m, 1H), 1.40 (d, J=6.5Hz, 3H); 1.28 (d, J=14.0 Hz, 6H); 0.69-0.74 (m, 1H, -cp), 0.49-0.56 (m,2H, -cp), 0.00-0.04 (m, 1H, -cp); ¹³C NMR (500 MHz, DMSO-d₆) δ 171.6,164.9, 161.4, 154.3 153.6, 152.3, 140.2, 109.6, 76.0, 74.0, 60.2, 51.4,29.4, 28.6, 21.1, 14.7, 11.0, 7.3; ³¹P NMR (CDCl₃, 202 MHz): δ 2.67,2.99. HR-MS Calcd. For (C₂₄H₃₂N₃O₉P+H)⁺ 537.1876, found 537.1942.

Detailed Synthetic Protocols for FIG. 3(−)-(((3aR,4S,6R,6aR)-4-(benzyloxy)-2,2-dimethyltetrahydrospiro[cyclopenta[d][1,3]dioxole-5,1′-cyclopropan]-6-yl)methoxy)(tert-butyl)dimethylsilane(23)

To a stirred solution of 12 (5.5 g, 16.7 mmol) in anhydrous DMF (50 mL)was added NaH in 60% mineral oil (0.8 g, 20.1 mmol), at 0° C. underargon. After 30 minutes benzyl bromide (2.36 mL, 20.1 mmol) was addeddrop wise at same temperature. The mixture was stirred for 3 hr at roomtemperature. It was quenched with ice-cold water (50 mL) and extractedwith diethyl ether (2×300 mL). The combined extracts were washed withwater (200 mL), brine (100 mL) and dried over Na₂SO₄. The solvent wasremoved under reduced pressure and the residue was purified by flashsilica gel column chromatography (EtOAc:Hexane 1:10 to 3:10) to givefully protected carbocyclic intermediate 24 (5.6 g 80%) as oil. [α]²⁴_(D)−121.09° (c 0.83, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ 7.43 (m, 5H),4.83 (d, J=12.5 Hz, 1H), 4.68 (d, J=12.5 Hz, 1H), 4.56 (t, J=5.5 Hz,1H), 4.44 (d, J=6.0 Hz, 1H), 4.30 (m, 1H), 3.42 (dd, J=4.0, 8.5 Hz, 1H),3.21 (dd, J=5.0, 8.5 Hz, 1H), 2.59-2.57 (m, 1H), 1.46 (s, 3H), 1.34 (s,3H), 0.84 (m, 10H), 0.43 (m, 1H), 0.32 (m, 1H), 0.24 (m, 1H), −0.06 (s,6H); ¹³C NMR (125 MHz, CDCl₃) δ 150.6, 138.6, 127.8, 110.8, 108.9, 81.3,79.7, 78.5, 72.6, 71.8, 64.5, 49.9, 32.13, 31.54, 30.33, 29.24 23.83,7.14, 0.015; HR-MS Calcd. For (C₂₁H₃₀O₄+H)⁺ 419.2539, found 419.2831.

(−)-(4S,5R,6R,7R)-4-(benzyloxy)-7-(hydroxymethyl)spiro[2.4]heptane-5,6-diol(24)

The fully protected resultant carbocyclic intermediate 23 (5.6 g, 13.3mmol) was dissolved in 100 mL of CF₃CO₂H/H₂O (2:1, v/v) and heated to50° C. for 3 h. The solvent was removed under vacuum and the residue wasco-evaporated with ethanol (3×50 mL). The residue dissolved in methanol(100 mL) and passed ammonia gas at 0° C. for 5 minutes forneutralization. After removal of the solvent the residue was purified bysilica gel column chromatography (3% MeOH/DCM) to give 5 (2.9 g, 82%) asa white solid. mp 122-124° C.; [α]²⁴ _(D)−123.05° (c 0.37, MeOH); ¹H NMR(500 MHz, CD₃OD) δ 7.46-7.30 (m, 5H), 4.77 (d, J=12 Hz, 1H), 4.62 (d,12.5 Hz, 1H), 4.17-4.14 (m, 2H), 3.95-3.93 (m, 1H), 3.82-3.73 (m, 2H),2.69-2.66 (m, 1H), 0.61 (m, 1H), 0.43 (m, 1H), 0.32 (m, 1H), 0.24 (m,1H); ¹³C NMR (125 MHz, CDCl₃) δ 148.9, 138.3, 128.0, 109.1, 80.8, 71.7,71.0, 70.8, 61.8, 49.6, 29.24 23.83, 7.14; HR-MS Calcd. For(C₁₅H₂₀O₄+H)⁺ 265.1362, found 265.1410.

(−)-(6aR,8S,9S,9aR)-8-(benzyloxy)-2,2,4,4-tetraisopropyltetrahydro-6H-spiro[cyclopenta[f][1,3,5,2,4]trioxadisilocine-7,1′-cyclopropan]-9-ol(25)

To a stirred mixture of triol 24 (2.9 g, 10.9 mmol) and imidazole (5.2g, 76.8 mmol) in DMF (80 mL) at 0° C. under argon was added dropwise1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane (3.5 mL, 11.0 mmol). Afterthe mixture was stirred at room temperature for 1 h, quenched with MeOH(15 mL) and water (100 mL) was added and the mixture was extracted withEtOAc (2×200 mL). The combined organic layers were washed with brine (40mL) dried over Na₂SO₄. The solvent was removed and the residue waspurified by silica gel column chromatography (EtOAc:Hexane 1:30 to 1:5)to give 25 (5.1 g, 92%) as an oil. [α]²⁴ _(D)−105.94° (c 0.58, CHCl₃);¹H NMR (500 MHz, CDCl₃) δ 7.41-7.26 (m, 5H), 4.77 (d, J=12 Hz, 1H), 4.62(d, J=12 Hz, 1H), 4.18-4.14 (m, 3H), 4.05 (dd, J=4.5, 12.0 Hz, 1H), 3.78(dd, J=8, 12 Hz, 1H), 2.89 (m, 1H), 2.78 (d, J=2.0 Hz, 1H, OH) 1.08-0.97(m, 28H), 0.61 (m, 1H), 0.43 (m, 1H), 0.32 (m, 1H), 0.24 (m, 1H); ¹³CNMR (125 MHz, CDCl₃) δ 154.0, 147.3, 138.1, 128.4, 80.2, 74.2, 71.2,71.1, 64.9, 50.1, 29.24 23.83, 17.6, 17.5, 17.4, 17.3, 17.2, 17.1, 17.0,16.9, 16.8, 13.4, 12.9, 12.7, 12.5. 7.20; HR-MS Calcd. For(C₂₇H₄₆O₅Si₂+H)⁺ 507.2884, found 507.2798.

(−)-(6aR,8S,9R,9aR)-8-(benzyloxy)-9-fluoro-2,2,4,4-tetraisopropyltetrahydro-6H-spiro[cyclopenta[f][1,3,5,2,4]trioxadisilocine-7,1′-cyclopropane](26)

To a solution of alcohol 25 (5.1 g, 10.7 mmol) in anhydrous CH₂Cl₂,(diethylamino) sulfur trifluoride (DAST) (9.3 ml, 70.5 mmol) was addedslowly at room temperature. The reaction mixture was quenched with icedH₂O after 20 min. The organic layer was collected and the aqueous phasewas extracted with dichloromethane. The organic layer was then combined,dried over Na₂SO₄ and the volatiles removed under reduced pressure. Thecrude residue was purified by flash silica gel column chromatography (1%EtOAc/Hexane) to give 26 (2.5 g, 49%). [α]²⁴ _(D)−98.08° (c 0.51,CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ 7.39-7.26 (m, 5H), 4.92 (ddd, J=6.0,7.5 & 5.5 Hz, 1H), 4.78 (d, J=11.5 Hz, 1H), 4.65 (d, J=11.5 Hz, 1H),4.31-4.26 (m, 1H), 4.23-4.16 (m, 1H), 4.01-3.92 (m, 2H), 2.70 (m, 1H)1.08-0.94 (m, 28H), 0.72 (m, 1H), 0.68-0.43 (m, 2H), 0.28 (m, 1H); ¹³CNMR (125 MHz, CDCl₃) δ 142.6 (d, J=9.2 Hz), 141.8, 137.9, 128.4, 112.7,103.4 (d, J=189.0 Hz), 80.4 (d, J=21.3 Hz), 73.8 (d, J=19.8 Hz), 71.3,61.6, 48.8 (d, J=5.3 Hz), 29.4, 24.5, 17.5, 17.4, 17.3, 17.2, 17.1,17.0, 16.9, 16.8, 13.4, 13.3, 12.7, 12.5, 7.9; HR-MS Calcd. For(C₂₇H₄₅FO₄Si₂+H)⁺ 509.2840, found 509.2923.

(−)-(6aR,8S,9R,9aR)-9-fluoro-2,2,4,4-tetraisopropyltetrahydro-6H-spiro[cyclopenta[f][1,3,5,2,4]trioxadisilocine-7,1′-cyclopropan]-8-ol.(27)

A solution of compound 26 (1.38 g, 2.6 mmol) in anhydrous CH₂Cl₂ wastreated with boron trichloride (7.1 ml, 1M solution in CH₂Cl₂, 8.1 mmol)at −78° C. during 15 minute. After stirred at the same temperature foranother 15 min, additional portion of boron trichloride (5.1 mL of 1Msolution in CH₂Cl₂) was added. The reaction was quenched with MeOH at−78° C. after 15 min and concentrated under reduced pressure. Theresidue was purified by column chromatography on the silica gel(EtOAc:Hexane=1;10 to 1:3) to give 27 (0.84 g, 78%). [α]²⁴ _(D)−53.55°(c 0.5, MeOH); ¹H NMR (500 MHz, CDCl₃) δ 4.65 (dt, J=8.0 & 15.0 Hz, 1H),4.49-4.45 (m, 1H), 4.26-4.21 (m, 1H), 3.99 (dd, J=4.5 & 12.0 Hz, 1H),3.89 (dd, J=6.0 & 11.5 Hz, 1H), 2.66 (s, 1H), 0.93-1.08 (m, 28H), 0.72(m, 1H), 0.68-0.43 (m, 2H), 0.28 (m, 1H); ¹⁹F NMR (500 MHz, CDCl₃) δ−195.8 (m); ¹³C NMR (125 MHz, CDCl₃) δ 7.8, 12.5, 12.7, 13.3, 13.4,16.9, 16.98, 17.07, 17.08, 17.4, 17.5, 27.5 29.8, 49.1, 63.7, 73.7,74.7, 102.3 (d, J=192.7 Hz); HR-MS Calcd. For (C₂₀H₃₉FO₄Si₂+H)⁺418.2592, found 418.2592.

(−)-3-benzoyl-1-((6aR,8R,9R,9aR)-9-fluoro-2,2,4,4-tetraisopropyltetrahydro-6H-spiro[cyclopenta[f][1,3,5,2,4]trioxadisilocine-7,1′-cyclopropan]-8-yl)pyrimidine-2,4(1H,3H)-dione(28)

To a stirred solution of triphenylphosphine (0.37 g, 1.43 mmol), in THF(5 mL) at −10° C. was added dropwise the DIAD (0.26 mL, 1.43 mmol) andthe reaction mixture was stirred at this temperature for 30 min. Afterthat a solution of benzoyl protected uracil base (0.15 g, 0.7 mmol) inTHF (5 mL) was added and stirred for 30 minute at 0° C. Compound 27 (0.2g, 0.47 mmol) in THF (5 mL) was added and the reaction was stirred for 3hours at room temperature. The volatiles were removed under reducedpressure and the residue was purified by the silica gel columnchromatography (EtOAc:hexane=1:20 to 1:10) to give 28 (200 mg, 51%) ascolorless oil. UV (MeOH) λ_(max) 264 nm, (pH 7); 266.0 nm (pH 12); ¹HNMR (500 MHz, CDCl₃) δ 7.86 (d, J=12.5 Hz, 1H) 7.65-7.44 (m, 5H), 5.89(d, J=30.5 Hz, 1H), 5.76 (d, J=14.5 Hz, 1H), 4.80 (m, 1H), 4.65 (m, 1H),3.44-3.22 (m, 2H), 2.39 (m, 1H), 1.11-1.09 (m, 28H), 0.72 (m, 1H),0.68-0.43 (m, 2H), 0.28 (m, 1H); ¹⁹F NMR (500 MHz, CDCl₃) δ −192.87 (m);¹³C NMR (125 MHz, CDCl₃) δ 162.2, 153.6. 152.2, 144.1, 133.9, 128.6,113.4, 93.4, (d, J=187.5 Hz), 83.9, 76.0 (d, J=50.0 Hz), 64.3, 58.5,29.8, 27.8, 17.08, 17.07, 17.05, 16.09, 16.06, 13.05, 13.03, 8.1; HR-MSCald. For (C₃₁H₄₅FN₂O₆Si₂+H)⁺ 617.2800, found 617.2917.

1-((4R,5R,6R,7R)-5-fluoro-6-hydroxy-7-(hydroxymethyl)spiro[2.4]heptan-4-yl)pyrimidine-2,4(1H,3H)-dione(29)

Compound 28 (0.2 g, 0.32 mmol) was dissolved in saturated MeOH with NH₃(20 mL) and stirred for 8 h at room temperature. The solvent wasevaporated under vacuum and the residue was purified by silica gelvacuum column (35% EtOAc/hexane) to give the debenzolated compound.Debenzoylated compound was dissolved in 10 mL of CF₃COOH/H₂O (2:1, v/v)and heated to 50° C. for 3 h. The solvent was removed under vacuum andthe residue was co-evaporated with ethanol (3×10 mL) under vacuum. Theresidue was purified by combiflash chromatography (7% MeOH/CH₂Cl₂) togive 29 in 60 mg (68%) as white foam. [α]²⁴ _(D) 5.4° (c 0.67, MeOH); ¹HNMR (500 MHz, DMSO-d₆) δ 11.17 (bs, 1H), 7.68 (d, J=15.6, 1 H), 5.80 (d,J=19.7, 1H), 5.67 (d, J=14.5 Hz, 1H), 4.74-4.78 (bs, 2H, —OH), 4.70 (m,1H), 4.10-4.13 (bm, 1H, —OH), 3.32-3.43 (m, 2H), 2.1-2.08 (m, 1H),0.69-0.74 (m, 1H), 0.49-0.56 (m, 2H), 0.43 (m, 1H); ¹³C NMR (500 MHz,MeOH-d4) δ 164.9, 161.4, 152.3, 140.2, 109.6, 76.0, 74.0, 60.2, 51.4,21.1, 14.7, 11.0, 7.3; HR-MS Cald. For (C₁₂H₁₅FN₂O₄+H)⁺ 270.16, found270.1226.

Detailed Synthetic Protocols for FIG. 4(−)-(6aR,8S,9aR)-8-(benzyloxy)-2,2,4,4-tetraisopropyldihydro-6H-spiro[cyclopenta[f][1,3,5,2,4]trioxadisilocine-7,1′-cyclopropan]-9(6aH)-one(31)

To a stirred solution of alcohol 11 (4 g, 7.9 mmol) was added dessmartine (4.0 g, 9.4 mmol) at 0° C. The mixture was warm to ambienttemperature and stirred for 1 hr. The mixture was passed through celitebed and obtained filtrate was concentrated under reduced pressure. Theresidue was purified by column chromatography on a silica gel (2%EtOAc/hexane) to give ketone 31 (3.5 g, 89%) as an oil. [α]²⁴_(D)−98.94° (c 0.58, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ 7.41-7.26 (m,5H), 4.62 (d, J=12 Hz, 1H), 4.42 (d, J=12 Hz, 1H), 4.18-4.14 (m, 2H),4.05 (dd, J=4.5, 12.0 Hz, 1H), 3.78 (dd, J=8, 12 Hz, 1H), 1.98 (m, 1H),1.08-0.97 (m, 28H), 0.61 (m, 1H), 0.43 (m, 1H), 0.32 (m, 1H), 0.24 (m,1H); ¹³C NMR (125 MHz, CDCl₃) δ 162.2, 154.0, 147.3, 138.1, 128.4, 80.2,74.2, 71.2, 64.9, 50.1, 29.24 23.83, 17.6, 17.5, 17.4, 17.3, 17.2, 17.1,17.0, 16.9, 16.8, 13.4, 12.9, 12.7, 12.5. 7.20; HR-MS Calcd. For(C₂₇H₄₄O₅Si₂+H)⁺ 505.2727, found 505.2798.

(−)-(6aR,8S,9aR)-8-hydroxy-2,2,4,4-tetraisopropyldihydro-6H-spiro[cyclopenta[f][1,3,5,2,4]trioxadisilocine-7,1′-cyclopropan]-9(6aH)-one(32)

A solution of compound 31 (3.5 g, 6.9 mmol) in anhydrous CH₂Cl₂ wastreated with boron trichloride (20.5 ml, 1M solution in CH₂Cl₂, 21.5mmol) at −78° C. during 15 minute. After stirred at the same temperaturefor another 15 min, additional portion of boron trichloride (6.8 mL of1M solution in CH₂Cl₂, 7.1 mmol) was added. The reaction was quenchedwith MeOH at −78° C. after 15 min and concentrated under reducedpressure. The residue was purified by column chromatography on thesilica gel (EtOAc:Hexane=1;10 to 1:3) to give 27 (0.84 g, 78%). [α]²⁴_(D)−76.54° (c 0.5, MeOH); ¹H NMR (500 MHz, CDCl₃) δ 4.49 (d, J=8.0,1H), 4.23-4.12 (m, 1H), 3.99 (dd, J=4.5 & 12.0 Hz, 1H), 3.89 (dd, J=6.0& 11.5 Hz, 1H), 2.39 (m, 1H), 0.93-1.08 (m, 28H), 0.72 (m, 1H),0.68-0.43 (m, 2H), 0.28 (m, 1H); ¹⁹F NMR (500 MHz, CDCl₃) δ −195.8 (m);¹³C NMR (125 MHz, CDCl₃) δ 7.8, 12.5, 12.7, 13.3, 13.4, 16.9, 16.98,17.07, 17.08, 17.4, 17.5, 27.5 29.8, 49.1, 63.7, 74.7, 84.2, 164.2;HR-MS Calcd. For (C₂₀H₃₈O₅Si₂+H)⁺ 414.2258, found 414.2362.

Biological Data

The spiro[2.4]heptanes described herein exhibit significantanti-Flaviviridae, for example, anti-HCV activity. Compounds accordingto the present invention can be assayed for anti-Flaviviridae activity,especially anti-HCV activity, using well-known and conventional assaysfound in the literature.

For example, anti-HCV activity and cytotoxicity of the compounds may bemeasured in the HCV subgenomic RNA replicon assay system in Huh7 ETcells. (See, Korba, et al., Antiviral Research 2008, 77, 56). Theresults may be summarized in comparison to a positive control,2′-C-Me-cytosine {2′-C-Me-C}(Pierra, et al., Journal of MedicinalChemistry 2006, 49, 6614.

Another in-vitro assay for anti-hepatitis C activity is described inU.S. Pat. No. 7,718,790 by Stuyver, et al., and assigned to Pharmasset,Inc.

There are numerous literature assays for Dengue fever, West Nileencephalitis, Tick-borne encephalitis, and Yellow fever, includingStahla, et al., “Identification of a Novel Antiviral Inhibitor of theFlavivirus Guanylyltransferase Enzyme”, Journal of Virology, August2012, Vol 86 (16), pp 8730-8379.

This specification has been described with reference to embodiments ofthe invention. Given the teaching herein, one of ordinary skill in theart will be able to modify the invention for a desired purpose and suchvariations are considered within the scope of the invention.

I claim:
 1. A method for the treatment of a condition resulting from ahepatitis C infection, in a host in need thereof, comprisingadministering an effective amount of a spiro[2.4]heptane of thefollowing structure:

wherein: R¹ is a natural or non-natural heteroaryl or heterocyclicmoiety; R² is methyl or F; R³ is methyl, F, Cl, N₃, or OR⁷; R⁴ is OR⁷,H, methyl, F, Cl, or N₃; R⁵ is H, phosphate, a stabilized phosphateprodrug, phosphoramidate, acyl, alkyl, sulfonate ester, a lipid, aphospholipid, an amino acid, a carbohydrate, a peptide, a cholesterol,or other pharmaceutically acceptable leaving group which whenadministered in vivo is capable of providing a compound wherein R⁵ is Hor mono, di, or tri-phosphate; and, R⁷ is H, acyl, phosphate, sulfate,amino acid, peptide, or an oxygen-protecting group; or itspharmaceutically acceptable salt; optionally in a pharmaceuticallyacceptable carrier.
 2. The method of claim 1, wherein R¹ is a pyrimidineor purine.
 3. The method of claim 2, wherein the purine or pyrimidine isselected from the group consisting of cytosine, 5-halocytosine, uracil,5-halouracil, 5-methylcytosine, thymine, adenine, thymine, guanine,xanthine, or hypoxanthine.
 4. The method of claim 2, wherein thepyrimidine is 5-fluorocytosine or 5-fluorouracil.
 5. The method of claim2, wherein the pyrimidine is uracil.
 6. The method of claim 2, whereinthe pyrimidine is cytosine.
 7. The method of claim 1, wherein R⁵ is aphosphoramidate.
 8. The method of claim 2, wherein R² is methyl, R³ isF, and R⁴ is OR⁷.
 9. The method of claim 8, wherein R¹ is uracil. 10.The method of claim 9, wherein R⁵ is a phosphoramidate.
 11. The methodof claim 1, wherein the spiro[2.4]heptane is administered orally. 12.The method of claim 1, wherein the spiro[2.4]heptane is administeredtransdermally.
 13. The method of claim 1, wherein the spiro[2.4]heptaneis administered via controlled release.
 14. The method of claim 1,wherein the spiro[2.4]heptane is administered intravenously.
 15. Themethod of claim 1, wherein the condition resulting from a hepatitis Cinfection is an antibody positive and antigen positive condition,viral-based chronic liver inflammation, liver cancer resulting fromadvanced hepatitis C, cirrhosis, or fatigue.
 16. The method of claim 1,further comprising administering the spiro[2.4]heptane in combinationwith another anti-HCV agent.
 17. The method of claim 16, wherein theadditional anti-HCV agent is selected from the group consisting of aprotease inhibitor; an NS5A inhibitor; another NS5B polymeraseinhibitor; a non-substrate (allosteric) inhibitor; interferon alfa-2a,which may be pegylated; ribavirin; a helicase inhibitor; an antisenseoligodeoxynucleotide (S-ODN); an aptamer; a nuclease-resistant ribozyme;iRNA; an antibody to HCV; a partial antibody to HCV; and a domainantibody to HCV.
 18. A method for treating a condition resulting from ahepatitis C infection, in a host in need thereof, comprisingadministering an effective amount of spiro[2.4]heptane of the followingformula:

wherein R¹, R², R³, R⁴, R⁵, and R⁷ are as defined in claim 1, or apharmaceutically acceptable salt thereof; optionally in apharmaceutically acceptable carrier.
 19. The method of claim 18, whereinthe condition resulting from a hepatitis C infection is an antibodypositive and antigen positive condition, viral-based chronic liverinflammation, liver cancer resulting from advanced hepatitis C,cirrhosis, or fatigue.
 20. The method of claim 18, further comprisingadministering the spiro[2.4]heptane in combination with another anti-HCVagent.
 21. The method of claim 20, wherein the additional anti-HCV agentis selected from the group consisting of a protease inhibitor; an NS5Ainhibitor; another NS5B polymerase inhibitor; a non-substrate(allosteric) inhibitor; interferon alfa-2a, which may be pegylated;ribavirin; a helicase inhibitor; an antisense oligodeoxynucleotide(S-ODN); an aptamer; a nuclease-resistant ribozyme; iRNA; an antibody toHCV; a partial antibody to HCV; and a domain antibody to HCV.
 22. Themethod of claim 17, wherein the protease inhibitor is selected from thegroup consisting of telaprevir and boceprevir.
 23. The method of claim21, wherein the protease inhibitor is selected from the group consistingof telaprevir and boceprevir.
 24. The method of claim 1, furthercomprising administering the spiro[2.4]heptane in combination with ananti-hepatocellular carcinoma agent.
 25. The method of claim 24, whereinthe anti-cancer agent is selected from the group consisting of ananti-angiogenic agents, sunitinib, brivanib, linifanib, ramcirumab,bavcizumab, cediranib, pazopanib, TSU-68, lenvatinib, antibodies againstEGFR, mTor inhibitors, MEK inhibitors, and histone deacetylaseinhibitors.
 26. The method of claim 18, further comprising administeringthe spiro[2.4]heptane in combination with an anti-hepatocellularcarcinoma agent.
 27. The method of claim 26, wherein the anti-canceragent is selected from the group consisting of an anti-angiogenicagents, sunitinib, brivanib, linifanib, ramcirumab, bavcizumab,cediranib, pazopanib, TSU-68, lenvatinib, antibodies against EGFR, mTorinhibitors, MEK inhibitors, and histone deacetylase inhibitors.
 28. Themethod of claim 1, wherein R³ is F or R² is F.
 29. The method of claim1, wherein R⁴ and R⁵ together form a bridge.
 30. The method of claim 29,wherein the bridge is selected from a phosphoester, carbodiester, or aphosphoramidate.
 31. The method of claim 18, wherein R¹ is a pyrimidineor purine.
 32. The method of claim 31, wherein the purine or pyrimidineis selected from the group consisting of cytosine, 5-halocytosine,uracil, 5-halouracil, 5-methylcytosine, thymine, adenine, thymine,guanine, xanthine, or hypoxanthine.
 33. The method of claim 31, whereinthe pyrimidine is 5-fluorocytosine or 5-fluorouracil.
 34. The method ofclaim 31, wherein the pyrimidine is uracil.
 35. The method of claim 31,wherein the pyrimidine is cytosine.
 36. The method of claim 18, whereinR⁵ is a phosphoramidate.
 37. The method of claim 31, wherein R² ismethyl, R³ is F, and R⁴ is OR⁷.
 38. The method of claim 37, wherein R¹is uracil.
 39. The method of claim 38, wherein R⁵ is a phosphoramidate.40. The method of claim 18, wherein the spiro[2.4]heptane isadministered orally.
 41. The method of claim 18, wherein thespiro[2.4]heptane is administered transdermally.
 42. The method of claim18, wherein the spiro[2.4]heptane is administered via controlledrelease.
 43. The method of claim 18, wherein the spiro[2.4]heptane isadministered intravenously.
 44. The method of claim 18, wherein R⁴ andR⁵ together form a bridge.
 45. The method of claim 44, wherein thebridge is selected from a phosphoester, carbodiester, or aphosphoramidate.
 46. The method of claim 17, wherein the additional NS5Bpolymerase inhibitor is PSI-7977.
 47. The method of claim 21, whereinthe additional NS5B polymerase inhibitor is PSI-7977.
 48. The method ofclaim 18, wherein R² is F or R³ is F.
 49. A method for the treatment ofa condition resulting from a hepatitis C infection, in a host in needthereof, comprising administering an effective amount of aspiro[2.4]heptane of the following structure:

wherein: R¹ is a natural or non-natural heteroaryl or heterocyclicmoiety; R² is H; R³ is F; R⁴ is OR⁷, H, methyl, F, Cl, or N₃; R⁵ is H,phosphate, a stabilized phosphate prodrug, phosphoramidate, acyl, alkyl,sulfonate ester, a lipid, a phospholipid, an amino acid, a carbohydrate,a peptide, a cholesterol, or other pharmaceutically acceptable leavinggroup which when administered in vivo is capable of providing a compoundwherein R⁵ is H or mono, di, or tri-phosphate; and, R⁷ is H, acyl,phosphate, sulfate, amino acid, peptide, or an oxygen-protecting group;or its pharmaceutically acceptable salt; optionally in apharmaceutically acceptable carrier.